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The Messenger
No. 154 – December 2013
P a r a n
a l i n s t r u m e n t a t i o n p r o
g r a m m e
F o c u s o n E S O
P u b l i c S u r v e
y s
R e s o
l v i n g A G N
w i t h M I D I
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3The Messenger 154 – December 2013
instruments. The second phase is dic-tated by the strategy of
how the VLT willbe used in the E-ELT era.
Phase 1 (Projects initiated before 2018/ deployed before ~
2025). There is no indication that the size of theParanal user
community will decrease.On the contrary, new Member States
may join ESO, increasing the pressure onthe Paranal
facilities. Consequently thescientic use and output of
Paranalinstruments should be optimised. It isimportant to preserve
a balance betweenspecialised instruments and workhorseinstruments,
with the latter covering awide range of scientic interests.
Phase 2 (Long-term opportunities in theE-ELT era, af ter ~
2025). This phase is still re latively open anddifferent
scenarios can be envisaged. The E-ELT will be fully
operational andastronomical research with 8-metre-class telescopes
may evolve towards amodel where a large fraction of the timeis
devoted to dedicated experimentsand large collaborative projects.
In thiscontext the four VLT Unit Telescopestogether could provide a
unique oppor-tunity to dedicate up to ~ 1200 nightsper year to a
single problem. Thisapproach could open up new perspec-tives in
astronomical research. The lasttwo instruments of the decade
(deployedin 2018/2019), should be fully integratedinto this
long-term perspective. Theirselection will occur after a careful
reec-tion on the scientic use and role of the VLT in the E-ELT
era. To this purpose,several scientic conferences will be heldin
the coming years to direct the choicesand nalise the strategy and
its imple-mentation.
Programmatic drivers
The instrumentation development planfollows from
consideration of a numberof basic drivers:
Paranal and E-ELT The E-ELT will be an additional
telescopeat the Paranal Observatory, and the
strengths of each unit should be maxim-ised. Synergy and the
ability to comple-ment E-ELT capabilities are thereforeimportant
criteria for the VLT.
Paranal, HST and JWSTBy 2018 the Hubble Space Telescope(HST)
will most likely no longer be inoperation, and the James Webb
Space Telescope (JWST ) will be about toenter operations. HST
capabilities thatwill be unavailable include ultraviolet(UV)
spectroscopy and high-resolutionimaging in the B- to R-bands. An
instru-ment able to provide diffraction-limitedobservations in the
B- to R-bands overa sufciently large eld could recoveran important
part of the missing parame-ter space. Complementarity betweenthe
VLT and the JWST in the areas ofhigh resolution spectroscopy,
observationof bright sources, diffraction-limitedobservation at
short wavelengths, exibleoperations, wide wavelength coverageand
use of wide eld can be mentioned.It may also be advantageous to
providesome overlapping capabilities with JWST.
Paranal and ground-based observatories The relationship of
Paranal with otherground-based observatories (including ALMA)
has sti ll to be discussed in depth.In general, the Paranal choices
will bedriven by the scientic requests of theESO community rather
than by the devel-opments of its competitors.
Maximisation of efciency/optimal useof observing
timeOptimisation can be achieved by concen-trating on three main
aspects: improvedefciency (throughput and duty cycle);extending the
spectral coverage; explor-ing the possibilities for sharing the
availa-ble foci. This goal could include the con-cept (new for the
VLT) of instrumentsdesigned to be exchanged with a
regularcadence.
Instrument development duration The typical development
time for secondgeneration VLT instruments has beenalmost ten years
from the time of con-ception. This long lead time should notbe
assumed to be inevitable, and theprogramme could develop
instrumentson shorter construction times if thisbecomes an agreed
goal. One interestingpossibility would be to create a newclass of
visitor instrument, operated bythe construction team, but also
includ-ing proposals from the community atlarge (in the manner of
the VLTI instru-ment PIONIER).
Focus occupancyWith the arrival of ESPRESSO in 2016,all VLT/I
foci will be occupied, includingthe incoherent combined focus.
Someinstruments (e.g., ISAAC and MIDI) willhave been decommissioned
as earlyas 2013–2014 and replaced by secondgeneration instruments
(SPHERE, MUSEand GRAVITY). Each time a new instru-ment is accepted,
the instrument to bedecommissioned will be identied on thebasis of
a grid of criteria that includes:scientic potential,
complementarity withnew instruments, instrument status andfuture
perspectives.
Role of La SillaIt is clear that today the success
of4-metre-class telescopes is often linkedto the ability to occupy
scientic niches.HARPS at the ESO 3.6-metre telescopeis a good
example of such a successstory. The specic added value of theLa
Silla 4-metre-class telescopes for ESOcan be summarised:– La Silla
continues to be a competitive
site in the southern hemisphere pro-viding unique opportunities
to its users;
– the ESO community continues torequest the ESO 3.6-metre
telescopeand the New Technology Telescope(NTT) at reasonable to
high oversub-scription rates and both telescopescontinue to produce
good publicationrates (105 refereed publications fromthe NTT in
2012, 69 from the ESO 3.6-metre);
– the ESO 3.6-metre telescope and theNTT are maintained to VLT
technicalstandards and provide excellent imagequality and efciency
at negligible tech-nical down time;
– a minority of Member States haveaccess to national
4-metre-class tele-scopes;
– La Silla provides the opportunity todedicate a 4-metre-class
telescope toone, or a few, scientic questions;
– 4-metre-class telescopes with state-of-the-art (workhorse)
instrumentationrelease pressure on the observing timeat the VLT
(and in the future, possiblyfor the E-ELT).
Considering that the current NTT instru-mentation is reaching
the end of its lifecycle (EFOSC2 went into operation in1990, SOFI
in 1998), ESO will launch acall in 2014 for a new instrument for
the
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4 The Messenger 154 – December 2013
wavelength range by a large factor. Anupgrade that considers the
installationof a set of cross-dispersers and newdetectors has
passed Phase A and, afterpositive STC recommendation, is nowin the
design and construction phase(Oliva et al., 2012). It will answer a
numberof scientically pressing questions, andwill, in addition,
satisfy several of theabove considerations (such as
comple-mentarity with JWST and improvement ofefciency).
MOONS and 4MOST
The proposal to bui ld a new, powerfulmulti-object
spectrograph (MOS) hasbeen strongly endorsed by the ESO com-munity
and advocated in several instancesby the STC. After a call for
ideas, twocompetitive MOS Phase A studies wereawarded: 4MOST (de
Jong et al., 2011)and MOONS (Cirasuolo et al., 2011).
MOONS is a near infrared facility (0.8–1.8 μm) which can host up
to 1000 bresat the Nasmyth focus of the VLT. Theeld of view is
about 500 square arc-minutes. It can operate either at
lowerresolution (R ~ 5000) or at higher resolu-tion (R ~ 20 000) in
two selected spectralregions.
4MOST is proposed for the 4-metre VISTA telescope, with a
eld of view ofmore than 3 square degrees. It will hostup to 2400
bres and will work in theoptical (0.3–0.9 μm). Sixteen hundredbres
will feed two lower resolution spec-trographs (R ~ 5000), with 800
bresto two higher resolution spectrographs(R ~ 20 000).
These two instruments are largelycomplementary in almost
all aspects:spectral coverage, telescope used, eldof view and
scientic aims. Given theoutstanding science cases presented bythe
two consortia, the enormous rangeof applications of large eld
spectroscopyand the strong push by the communityto increase ESO’s
MOS capabilities,together with the strong complementaritywith JWST
and E-ELT, both instrumentshave been recommended for designand
construction by STC. The work for
MOONS has star ted in 2013 and 4MOSTwill start in 2014.
NTT to be built in the community. Thisnew instrument could
replace eitherSOFI or EFOSC2 or both, and would beavailable to the
ESO community for50% of the time until 2021. Additionalobserving
time with the new instrumentwill be available for interested
groupsthrough the co-funding of NTT opera-tions.
The NTT call wil l be open for both spe-cialised
instruments, taking advantageof the large amount of dedicated
ob-serving time, as well as state-of-the-artworkhorse instruments
addressing broadneeds within the ESO community. Suchan instrument
is required to be at negli-gible cost to ESO.
Instrument denition and procurementprocedure
Scientic input for the new instruments isprovided to the
instrumentation pro-gramme manager through:– the “Paranal in the
E-ELT era” white
paper, as well as other inputs from the VLT programme
scientist;
– the community, by either contacting theinstrumentation
programme managerdirectly, via the STC, or via ad
hoc sci-entic conference(s).
Each proposal will be scientically evalu-ated by the VLT
programme scientist.In order to ensure community input to
thedenition of the Paranal instruments, sci-entic workshops will be
organised toaddress the scientic needs for the VLT inthe next
decade. The emphasis will beon 8-metre telescope science rather
thaninstruments or technological concepts. These workshops,
organised in theperiod 2013–2017, will dene the instru-mental
capabilities to be developed after~ 2018.
A working group of about 15 people(ve from ESO, ve
composed of STCmembers and ve community experts)will evaluate the
best sequence in whichto deploy the 2015–2018 projects.
Anon-exhaustive list of instrument options,which has emerged so far
from the dif-ferent inputs, is presented in the
followingsections.
After the var ious inputs have been col-lected and
elaborated, a proposalconsisting of the top-level
characteristicsfor the instruments will be presentedto the STC.
Once the concept has beenrecommended a call for tenders forPhase A
study will follow.
The Paranal instrumentation programmewill not be static,
and must be able toreact to the evolving scientic and
tech-nological landscape and to re-assignpriorities. New proposals
will be evalu-ated by the programme manager, in col-laboration with
ESO management andthe STC, against the existing
plan. Acceptance of a new project may resulteither in
cancelling/de-scoping or re-phasing planned projects. A similar
evalu-ation will be made if one of the runningprojects requests a
substantial increasein the allocated resources.
New instruments for the VLT
Following a series of Phase A studiesand recommendations by the
STC, thefollowing new instruments are now inprocess.
CUBESIn UV spectroscopy from the ground(i.e., 300–380 nm
spectral range), alarge increase of efciency with respectto the
existing instruments (UVES and X-shooter) is possible. In
addit ion, thisspectral range complements that of theE-ELT and
JWST. An efcient UV spec-trograph can cover a broad sciencecase and
could be a world-leading instru-ment for many years to come.
Locatedat the Cassegrain focus, it could be easilyexchanged. The
CUBES concept will bedeveloped by a consortium of
Brazilianinstitutes and ESO. The project haspassed Phase A review
and has beenrecommended by the STC. The detaileddesign is ongoing,
and constructionwill commence following the raticationof Brazilian
accession to ESO.
CRIRES upgradeCRIRES is equipped with a pre-disperserand
currently delivers a fraction of oneechelle order per observation.
A cross-disperser could increase the simultaneous
Telescopes and Instrumentation Pasquini L. et a l.,
Paranal Instrumentation Programme
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Potential new instruments for the VLT/I
After examining the current complementof Paranal
instruments at the telescope,or in construction, a number of
potentialdevelopments can be identied, whichare listed below. This
list is not intendedto be exhaustive.
Workhorse instrument to complement/ support FORS2 and
X-shooterFORS2, X-shooter and ISAAC (and alsoEFOSC at the NTT) are
among themost popular and productive ESO instru-ments. They are
typical workhorses andthe user pressure on them is very high.It is
important that ESO preserves thisclass of instrument. With the
decommis-sioning of ISAAC, infrared spectroscopyin the 2.4–5 μm
regime will no longerbe available. Should the new workhorsebe a
multi-function mul ti-wavelengthinstrument? Or a copy (perhaps
slightlymodied) of one of the existing, mostrequested instruments?
Such questionswill be debated by the ESO/STC/commu-nity working
group.
New Instrument for the AOFIn answer to the STC request for a
planfor AO instruments at the VLT, ESOhas proposed a development in
twophases: ERIS, that will follow-up NACOand feed SPIFFI, the
SINFONI spectro-graph; a new, ambitious instrument,still to be
decided, to fully exploit thepotential of the AOF, in the focus
occu-pied by GRAAL and HAWK-I. A highStrehl B- to R-band imager
would be oneattractive possibility. A multi-IFU, AO-assisted, large
eld spectrograph wouldalso be unique, and its scientic meritsshould
be studied.
In either case, the instrument may requirea considerable amount
of research anddevelopment. The scientic discussionabout a new
AO-assisted instrument ofthis type should start soon.
New VLTI instrument
The VLTI wil l continue to provide thehighest angular
resolution, even in the
E-ELT era. The rising demand for imagingcapability of stellar
sur faces, close cir-
cumstellar environments and extra-galactic sources sets a clear
path forthe VLTI medium-term developmentplan. PIONIER, GRAVITY,
MATISSE andthe second generation fringe trackerare, and will be,
the immediate answersto that request. The continuous andsuccessful
effor t to improve the VLTI’srobustness and performance will
beessential too.
However, improving the spectral cover-age (visible to
mid-infrared) and the imag-ing capability of VLTI should remain
ahigh priority in the years to come. PIONIERalready provides this
and GRAVITY willprovide observing modes close to themost demanded
AMBER ones, but withgreater sensitivity and much improvedFourier
uv-plane coverage.
While it seems premature to star t a newproject given the
enormous ongoingeffort to complete and operate PRIMA,GRAVITY and
MATISSE, some avenuesto be explored for the VLTI in the comingyears
include:1) Securing the continuity of PIONIER and
offering it to the community;2) Continuing to offer a visitor
focus at the
VLTI;3) Exploring the six-telescope imaging
capabilities of VLTI with the existinginfrastructure.
Potential VLT instrument upgrades
Even if most of the VLT/I instruments willbe new or recently
upgraded, the 15 yearsof VLT experience demonstrate that thereare
frequent requests for upgrades(mostly of detectors) and that these
haveserved the community very well.Upgrades under consideration
are:– X-shooter: Two proposals to upgrade
X-shooter have been submitted andhave been evaluated.
– FORS2: A proposal to upgrade theFORS2 detector is being
prepared. The use of a 4kx4k pixel CCD detectorwould bring
substantial operationalbenets.
– SPHERE: The deformable mirror is for-mally below specication,
and areplacement could be needed if its per-formance
deteriorates.
All major upgrades will be treated as anyother project,
and compared to runningor planned instruments in order to
decidepriorities. It must be clear that startingone project per
year implies that either anew instrument or a major upgrade canbe
initiated, but not both.
Potential new instruments for La Silla
3.6-metreIn 2014 HARPS will be equipped with theLaser Frequency
Comb (LFC), but willbe out-performed by ESPRESSO at the VLT
after ~ 2017. However HARPShas the advantage of using a
dedicatedtelescope and of having built up a longtime-series of
observations; it shouldbe used for the sources that do not needan
8-metre collecting area. HARPS ishighly requested, and its future
demandwill also depend on the fate of space mis-sions. It is worth
recalling that exoplanetscience is a young and expanding eld.
NTT The new instrument for the NTT (seeabove) could either
be a dedicated instru-ment or a multi-function workhorse.
An exciting approach could be to com-plement HARPS at the
ESO 3.6-metrewith a near-infrared planet-nder atthe NTT, matching
the RV precision ofHARPS. Several observatories areplanning
instruments of this kind in thenorthern hemisphere. High velocity
pre-cision could make it unique.
An X-shooter-type instrument for theNTT could be an
interesting alternativeto EFOSC2 plus SOFI.
Roadmap
Starting from 2013, the resources dedi-cated to E-ELT
instrumentation willprogressively increase. This will imply
aprogressive decrease in the resourcesavailable for the Paranal
instrumentationprogramme to a new level that cansustain the “one
new start per year” plan. Table 1 shows the proposed t
imetable.For all instruments, one year of Phase Ais foreseen and a
development time
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6 The Messenger 154 – December 2013
of ve years. This is on the short side,but not unrealistic.
Figure 2 shows theParanal instrumentation and the
projectdevelopment in 2019 according to thepresent plan. In a
resource-constrainedenvironment, the beginning of new
pro- jects will also have to be subject to satis-factory
completion of existing projects.If existing projects run late, the
new oneswill be re-planned accordingly.
References
Cirasuolo, M. et al. 2011, The Messenger, 145, 11de Jong, R. et
al. 2011, The Messenger, 145, 14Oliva, E. et al. 2012, Proc. SPIE,
84462N
Links
The agendas of Council and STC meet ings can befound on
the ESO web pages:
http://www.eso.org/ public/about-eso/committees /
Telescopes and Instrumentation Pasquini L. et a l.,
Paranal Instrumentation Programme
Figure 2. PlannedParanal instrumentationin 2019. One new
instru-ment in integration, fourin design and construc-tion and one
in Phase Aare also planned at thistime (see Table 1).
Table 1. Proposeddevelopment plan forthe Paranal
instrumen-tation programme.One year of Phase A isexpected to be
carriedout, and the overallduration is typically esti-mated as six
to sevenyears. Delivery in thelast column refers tostart of
integration inParanal for instrumentsor to the end of the
inte-gration for infrastructureprojects (such as the
AOF and VLTI).
Year
2012
2013
2014
2015
2016
2017
2018
2019
2020
Phase A
CUBESCRIRES upgrade
Letter of interestNTT
New I (NTT?)
New II
New III
New IV
New V
New VI
Design & Construction
ERIS
MOONSCRIRES upgrade
4MOST
CUBES (?)
New I (NTT?)
New II
New III
New IV
New V
Delivery
KMOS VIMOS upgrade
MUSESPHERE
VISIR upgradePRIMA astrometryGRAVITYLFC for HARPS
AOFMATISSE
ESPRESSO VLTI
CRIRES upgrade
CUBES(?)MOONS
ERIS4MOST
New I (NTT?)
UT1 (Antu)
CRIRESKMOSFORS2
UT2 (Kueyen)
UVESMOONS X-shooter
UT3 (Melipal)
VIMOSSPHERE VISIR/CUBES
VISTA
4MOST
VLTI
AmberGRAVITY MATISSEPRIMA
UT4 (Yepun)
MUSEHAWK-IERIS AOF
ESPRESSO
http://www.eso.org/public/about-eso/committeeshttp://www.eso.org/public/about-eso/committeeshttp://www.eso.org/public/about-eso/committeeshttp://www.eso.org/public/about-eso/committees
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Telescopes and Instrumentation
Revisiting the Impact of Atmospheric Refraction on
VIMOS-MOS Observations: Beyond the Two-hour Angle
Rule
Rubén Sánchez-Janssen1
Fernando Selman2
Steffen Mieske2
Paul Bristow2
Peter Hammersley2
Michael Hilker2
Marina Rejkuba2
Burkhard Wolff2
1 NRC Herzberg Institute of Astrophysics,Canada
2 ESO
Multi-object spectroscopic (MOS)observations with VIMOS have
tradi-tionally been limited to a narrowtwo-hour range from the
meridian tominimise slit losses caused by atmos-pheric dispersion
and differentialrefraction. We revisit the impact ofthese effects
on the quality of VIMOS-MOS spectra through extensive simu-lations
of slit losses. We show thatMOS observations can be
effectivelyextended to plus/minus three hoursfrom the meridian for
elds with zenithangles smaller than 20 degrees atculmination —
provided a nonstandardrotator offset angle of 0 degrees isused. The
increase in target observabil-ity will enhance the efciency of
opera-tions, and hasten the completion ofprogrammes — a
particularly relevantaspect for the forthcoming spectro-scopic
public surveys with VIMOS.
Atmospheric refraction in VIMOS-MOSobservations
VIMOS (Le Fevre et al., 1998) is a wideeld-of-view (four
elds of 7 by 8 arc-minutes) instrument with imaging, integraleld,
and multi-object spectroscopiccapabilities mounted at the Nasmyth
Bfocus of the Very Large Telescope (VLT)Unit Telescope 3. The
instrument oper-ates in the optical wavelength range(360–1000 nm),
and is equipped with sixsets of grisms, six sets of broadbandlters,
plus three additional lter setsspecically designed to be used in
com-bination with the grisms to block the
second-order spectra. During the last fewyears the instrument
performance hasbeen signicantly enhanced (seeHammersley et al.,
2012; 2013): changing
the detectors to red-sensitive, low-fringing CCDs; replacing the
HR-bluegrism set with higher throughput volumephase holographic
grisms; introducingan active exure compensation system;redesigning
the focusing mechanismand mask cabinet; and introducing a
newpre-image-less MOS mode (Bristow etal., 2013). All these
improvements havemade VIMOS a much more stable instru-ment, and
have extended its lifetime toprepare it for the start of the
spectro-scopic public surveys for which ESO hasrecently issued a
call.
Further work to improve the operationalefciency of the
instrument includes the
present study, which has, as its maingoal, to revisit the need
for restrictedobservability of targets only within plusand minus
two hours from the meridian in
the MOS mode — the two-hour anglerule. VIMOS is not equipped
with atmos-pheric dispersion compensators (ADCs),and MOS
observations are carried outusing multi-slit masks (see Figure 1).
Asa result, atmospheric dispersion (causedby the wavelength
variation of the indexof refraction of air) and eld
differentialrefraction (resulting from airmass varia-tions across
the eld of view [FoV]) intro-
duce a wavelength-dependent uxreduction, due to slit losses,
that cannotbe corrected. Unfortunately, eld rotationfurther
prevents the alignment of all slits
Figure 1. Example of a VIMOS nding chart for MOSobservations.
Each quadrant is 7 by 8 arcminutes,and they are separated by two
arcminute gaps.
Allocated sli ts are overplotted in blue. The blank
areas (upper right of each nding char t) are maskedout proposal
information.
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9The Messenger 154 – December 2013
a certain level of data compression.Following the previous work
by Cuby etal. (1998), we set the tolerance level
forlosses/distortions at 20%. In Figure 5 weshow the
declination–hour-angle pairs(colour-coded according to slit
orienta-tion) for which the median spectral d istor-tion (top row)
or median ux loss (bottom
row) across the VIMOS FoV remain belowthis tolerance value
during a one hourlong integration. It is evident that for
eldsculminating at small zenith distances the
larger distortions and ux losses occur atlarger HAs. Both the
amount of losses/ distortions, and the dependence on
dec-lination, increase for bluer wavelengths. On the other
hand, for the east–west(PA = 90 degree) orientation, we see thatat
xed HA there is a very strong depend-
ence on declination, but the behaviourattens towards redder
wavelengths. Theminimum of the loss/distortion distribu-tions
slightly decreases and moves
towards southern declinations at largerHAs. For any given grism,
there is verylittle dependence on HA (except for ex-treme
declinations). Finally, the depend-ence on declination of
losses/distortionsincreases towards bluer wavelengths.
Beyond the two-hour angle ruleExtracting simple rules from a
problemwith such a high dimensionality requires
Figure 2. Output simu-lated spectra for ninedifferent slit
positionsacross the VIMOS FoV.
These are the result of aone hour long integra-tion (–3
< HA < –2) on aδ = 0 degree eld usingthe LR-red grism
for aninput at spectrum. Ineach panel we show thespectra for two
differentslit orientations, as wellas the correspondingrelative ux
loss (f ) andspectral distortion (Δ).
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10 The Messenger 154 – December 2013
with targets at δ ~> −5 or δ ~
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11The Messenger 154 – December 2013
range. Figure 6 shows the new airmassconstraint limits for MOS
observationblocks. They have been signicantlyrelaxed for elds
culminating at smallzenith distances, thus increasing
targetobservability. This will enhance theefciency of operations,
and speed upthe completion of programmes — aparticularly relevant
aspect for the forth-coming spectroscopic public surveyswith VIMOS.
These recommendations forMOS observations have already been inplace
since September 2013. To denethe optimal slit position angle for
any spe-cic target declination and instrumentsetup, we refer the
users to the summaryplots in the slit losses report at
the VIMOS news section1.
References
Bristow, P. et al. 2012, The Messenger, 148, 13Cuby, J.-G. et
al. 1998, Proc. SPIE, 3355, 36Hammersley, P. et al. 2012, The
Messenger, 142, 8Hammersley, P. et al. 2013, The Messenger, 151,
2Le Fèvre, O. et al. 1998, Proc. SPIE, 3355, 8
Links
1 Report on VIMOS slit losses:
http://www.eso.org/
sci/facilities/paranal/instruments/vimos/doc/ rsjvimosslitlossessept2013.pdf
Figure 6. VIMOS airmass constrain ts for MO Sobserving
blocks. The two different shadedareas correspond to the limits for
elds thatcan be observed with slits having north–south
orientations at meridian (purple), or east–westorientations
(green). The generating formulaefor these curves are shown w ith
the samecolour coding.
Figure 5. Circles show thedeclination–hour-anglepairs
(colour-coded accord-ing to slit orientation —orange for
north–south andgreen for east–west) forwhich the median
spectraldistortion (top row) ormedian ux loss (bottomrow) across
the VIMOS FoVremain below 20% during aone hour long integration,for
all the VIMOS grisms.
–90 –80 –70
1.1
1
1.2
1.3
1.4
1.5
1.6
M a x i m u m a
l l o w e d a i r m a s s
1.7
1.8
1.9
Stay in the shaded area when specifying your airmass
constraint
VIMOS ai rmass constraints for MOS OBs
airmass ≤ 1/ (0.64280 cos δ – 0.41668 sin δ )airmass ≤
1/ (0.78726 cos δ – 0.41668 sin δ )
2
2.1
2.2
2.3
2.4
–60 –50 –40
Target decl inat ion (δ )
–30 –20 0 10 20 30–10
http://www.eso.org/sci/facilities/paranal/instruments/vimos/doc/rsjvimosslitlossessept2013.pdfhttp://www.eso.org/sci/facilities/paranal/instruments/vimos/doc/rsjvimosslitlossessept2013.pdfhttp://www.eso.org/sci/facilities/paranal/instruments/vimos/doc/rsjvimosslitlossessept2013.pdfhttp://www.eso.org/sci/facilities/paranal/instruments/vimos/doc/rsjvimosslitlossessept2013.pdfhttp://www.eso.org/sci/facilities/paranal/instruments/vimos/doc/rsjvimosslitlossessept2013.pdfhttp://www.eso.org/sci/facilities/paranal/instruments/vimos/doc/rsjvimosslitlossessept2013.pdf
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devices from e2v of high (but not perfect)cosmetic quality. In
addition to the32 CCDs making up the science array,OmegaCAM also
contains four auxiliaryCCDs around the edges of the eld thatare
used for autoguiding and imageanalysis. Since both guiding and
imageanalysis are performed on the instrumentside, the telescope
“only” tracks, butdoes so very well. Outside a zenith-centriccircle
of about 10 degrees diameter,image quality remains acceptable for
upto ~ 2–3 minutes without guiding.
Most data are taken in the ve Sloan-likebands
u, g, r , i and z , and a
narrow-band Hα lter provided by the VPHAS+consortium. Service
mode operations forOmegaCAM started on 15 October 2011. The
median full width at half maximum(FWHM) of OmegaCAM images,
asmeasured during the rst half year ofoperation, was about 0.80
arcseconds in i -band, and 0.95 arcseconds
in g-band(including the instrumental resolutionof 0.4
arcseconds). In the rst two yearsof operations, the sky was clear
or photo-metric 77% of the time.
Three public surveys are being executedat OmegaCAM (see
Figure 3): the Kilo-Degree Survey (KiDS; 1500 squaredegrees), ATLAS
(4500 square degrees),and the VST Photometric
Hα Survey(VPHAS+; 2000 square degrees). Fortheir detailed
setup and science goals,see the public survey web
pages2 and
Steffen Mieske1 Dietrich Baade1 Magda
Arnaboldi1 Giovanni Carraro1 Danuta
Dobrzycka1 Armin Gabasch1 Philippe
Gitton1 Nicolas Haddad1 Michael Hilker1 Ronald
Holzloehner1 Valentin D. Ivanov1 Sebastien
Morel1 Mark Neeser1 Loethe Noethe1
Ricardo Parra1 Andres Parraguez1 Monika
Petr-Gotzens1
Andrew Rakich1
Marina Rejkuba1 Miguel Riquelme1 Fernando
Selman1 Ricardo Schmutzer1 Thomas Szeifert1
1 ESO
The science operations process of the VLT Survey Telescope
(VST) camera,OmegaCAM, is described. OmegaCAMis a 267-megapixel CCD
camera imag-ing a 1 × 1 degree eld of view with apixel scale of
0.21 arcseconds. It beganoperations in October 2011. The tele-scope
and camera provide a surveyspeed that is ve times greater than
thenow-decommissioned Wide FieldImager on the MPG/ESO 2.2-metre
tele-scope at La Silla. OmegaCAM is cur-rently used for three
public surveys,
guaranteed time observations for theOmegaCAM and VST consortia,
andChilean programmes. The execution ofOmegaCAM observations,
real-timequality control and the calibration planare outlined.
General description of the facility
The VST resulted from a collaborationbetween the Italian
National Institute of Astrophysics ( INAF) under the
PrincipalInvestigator (PI) Massimo Capaccioli andESO (see
Capaccioli & Schipani [2011]for a description).
OmegaCAM1 was builtin a collaboration between ESO andthe
OmegaCAM consortium (PI, KonradKuijken) with contributions from
theNetherlands, Germany and Italy and isdescribed by Kuijken et al.
(2002) andKuijken (2011). With OmegaCAM ESOfullled its mandate from
the ESO Councilto provide an optical wide-eld imagingcapability at
Paranal Observatory.
OmegaCAM is the wide-eld imager forthe Cassegrain focus of the
VST onParanal. The VST is a 2.6-metre modiedRitchey–Chretien
alt-azimuth telescope(F/5.5) designed specically for
wide-eldimaging, to exploit the good image qualityat the Paranal
Observatory. OmegaCAMobserves from 330–950 nm within acorrected eld
of view of 1 × 1 degree,four times the size of the full
Moon.OmegaCAM samples the VST eld ofview with a 32-CCD, 16k × 16k
detectormosaic with 0.21-arcsecond pixel scale(Figure 2). The CCDs
are thinned, blue-sensitive, three-edge buttable CCD44-82
Telescopes and Instrumentation
OmegaCAM Science Operations
Figure 1. Left: The VST on the VLT platform. Right:OmegaCAM (the
yellow volume) mounted on the VST.
E S O / I N A F - V S T / O m e g a C A M / G .
L o m b a r d i
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the dedicated articles in this Messenger edition.
Releases of data from thesesurveys are available through Phase
33. The execution of these three sur veystakes up 50–60% of
the available servicemode time. The remaining 40–50% isshared
between guaranteed time obser-vations (GTO) for the OmegaCAM
and VST consortia, Chilean programmes, andcalibration
observations. The respectiveshares may evolve over time as a
functionof programme completion rates.
The survey speed of OmegaCAM isabout ve times higher than
the WideField Imager (WFI) at the MPG/ESO2.2-metre telescope in La
Silla (Baade etal., 1999). The good image qualit y andhigh blue
sensitivity provide a uniquewindow in observational parameter
space.Furthermore, it complements very well
the near-infrared survey telescope VISTAat Paranal (Emerson
& Sutherland, 2010),which is operated at the
neighbouringconsole in the VLT control room. VSTand VISTA together
cover the entire near-ultraviolet to near-infrared range 0.33–2.35
μm: VST from 0.33–0.95 μm, and VISTA from 0.85–2.35 μm, with
an over-lap at the z -band that is used by
bothfacilities.
Execution of observations
All observations on the VST are carr iedout in service
mode. The two surveyswith short integration times, VPHAS+
and ATLAS, observe most of the time in openloop (no guiding,
no image analysis). Dueto the high cadence of ~ 1–2 minutesbetween
images taken at different posi-tions on the sky in these two
surveys,there is no time to acquire image analysisstars and perform
active optics correc-tion at each new position. A new correc-tion
is enforced after, at most, half an
hour in such open loop observations. The KiDS survey spends
more time ona single pointing due to the sciencerequirement of
providing a deep andaccurate weak lensing map. KiDS obser-vations
are, therefore, performed withguiding and closed loop image
analysis.
The telescope and instrument are oper-ated at night by one
telescope operator,without a night-time astronomer. Theshort-term
scheduling of observations isdone by a program called the
Observing Tool (OT; see also Bierwir th et al.
[2010]). The basic observation unit containingthe full
description of the observationsequence (acquisition and science
expo-sures), information about the targetand the required observing
constraintsnecessary to achieve the scientic objec-tive, is called
an Observation Block (OB). At any given time, the OT lters out
allOBs that are not observable in the cur-rent conditions (due to
seeing, airmass,Moon illumination, sky transparency),and then ranks
the observable OBs tomatch, as well as possible, the
observingconditions requested by the users, while
Figure 2. Left: An image showing the 32 (4 × 8) CCDarray of
OmegaCAM and the four auxiliary CCDs usedfor guiding and wavefront
analysis. Right: OmegaCAMdome at illustrating individual chip
sensitivities, whichhave a root mean square chip-to-chip variation
of± 6%. The 32 science CCDs cover 92% of the1 × 1 degree eld of
view with only small inter-chipgaps. Dither patterns of a few
arcminutes total ampli-tude are used to image the full eld of
view.
Figure 4. Distinguished visitors at the VSTOmegaCAM console:
Chilean president SebastianPiñera and his wife. Also present in the
picture isParanal staff astronomer Fernando Selman.
Figure 3. The on-sky footpr int of the threepublic surveys
executed with OmegaCAM: KiDS(1500 square degrees), ATLAS (4500
square degrees),
VPHAS+ (2000 square degrees).
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suggests quality control grades for eachOB to the night-time
operator (see Fig-ure 6). Specically, the script calculates,for
each frame across the eld of view,the mean FWHM, the mean
ellipticity andthe IQ variation, which is the variationin the FWHM
in the centre of the eld vs.the FWHM at the edge of the eld ofview.
The script also measures the num-ber of single CCD images affected
byellipticities greater than 0.2. These num-bers are then
appropriately averagedacross an OB, or concatenation of OBs,and the
script suggests to the operatorthe zero-level quality control (QC0)
grades(fully/almost/not within constraints). Thegeneral QC0
acceptance criteria for anOB are: average seeing ≤ 1.1 ×
requestedseeing; average ellipticity ≤ 0.15; and IQvariation ≤
25%.
In addition to these criteria for a singleOB, the QC0 script
includes a number ofnested criteria regarding single
images,concatenations of OBs, special cases likeGTO and agreements
with consortiaabout deviations from the general QC0acceptance
criteria per OB. The scriptalso contains a number of warning
agswhich highlight image quality and cali-bration plan issues to
the operator. Thefull set of these criteria is quite complexand
could not realistically be trackedmanually by an operator during
the night. Therefore the QC0 script is a crucial partof
OmegaCAM science operations. Itallows fully reproducible quality
controlaccording to criteria agreed betweenESO and the users that
is as independentas possible from variations in humanhabits. An
example output is indicated inFigure 6, left panel.
taking into account relative programmepriorities (see Figure 5
for an exampleof the OT ranking). Users prepare theirOBs using the
P2PP4 software whichincludes the option to dene
relationsbetween OBs (groups, concatenationsand time series). Those
higher levelconstraints are also included in the rank-ing made by
the OT.
It is worth noting that around full Moonthere is a scarcity of
observable OBsdue to the bright sky background, whichmost of the
science cases for opticalimaging cannot tolerate. Also, only a
fewprogrammes accept the presence of thinclouds. The combination of
those twoissues has led to a comparably high frac-tion of 8–10%
idle time at the VST. ESOis taking measures to improve the bafingof
the VST which, in turn, will reduce theeffect of scattered
moonlight on the sci-ence images. More detail is provided inthe
section on challenges and outlook.
Real-time quality control during night-time observations
The high cadence of observations andlarge number of 32
CCDs (267 mega-
pixels) requires reliable automated qualitycontrol. With one
person operating boththe telescope and the instrument at night,it
is not possible to measure manuallyimage quality parameters across
the eldfor all those images, which can amountto several hundred per
night. Real-timequality control is performed by using theoutput log
of the OmegaCAM data reduc-tion pipeline, which was assembled byESO
from algorithmic modules providedby the OmegaCAM consortium.
Thereis a 1–2 minute delay between the com-pletion of an image and
the availabilityof the pipeline output log. This allowsnear
real-time assessment of data quali ty,enables fast decisions to be
taken tore-adjust the input parameters for the OTranking engine,
and hence optimise theobservation plan for the next
hour(s). The pipeline provides measurements ofmean point
spread function (PSF) FWHMand ellipticities for detected sources
ineach single chip.
The core of the automated qualit y contro lis a dedicated
script with some 800 linesof code which reads in the pipeline
out-put log, calculates the specic parame-ters that are used for
quality controlassessment (called QC0 at ESO), and
Telescopes and Instrumentation
Figure 5. Examplescreenshot of ObservingBlock ranking as
per-formed by the Observ-ing Tool.
Figure 6. Left: Example output of the real-time qual-ity control
script used for OmegaCAM. Each line cor-responds to one image. The
grouped sets of images
correspond to one OB or a concatenation of OBs.Right: PSF
anisotropy distribution for a single imageof average FWHM 0.65
arcseconds, taken in EarlyScience.
Mieske S. et al., OmegaCAM Science Operations
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The set of QC0 criteria appl ied toOmegaCAM night-time
observationsensures that we full our mission state-ment of
providing data of excellent imagequality to the users. This very
strictadherence to a combination of criterialeads to a slightly
larger rate of OB repe-titions than for other instruments:
forOmegaCAM, about 20% of time in ser-vice mode is spent on
repeating OBs(note that all data, whether in or out ofconstraints,
is immediately transferred tothe ESO archive). The typical
fractionfor other non-adaptive optics instrumentsat Paranal is
10–15%. Paranal instru-ments using adaptive optics, and
VLTinterferometer instruments, have agreater than 20% fraction of
time spenton repeating observations since they veryoften push out
to the instrumental andatmospheric limits. For OmegaCAM, thebalance
between strict QC0 and quickobserving progress is constantly
reviewedby the operations team in consultationwith the survey
consortia.
Calibration plan
The cal ibration plan of OmegaCAMensures continuous
monitoring of thesystem throughput in the
u, g, r , i and z -bands.
Sky ats are taken in two to
three lters during each clear eveningtwilight. Equatorial
Landolt photometricstandard star elds in
u to z -bands areobserved at the beginning and in
the
middle of the night. Furthermore, a shortobservation close to
the southern celes-tial pole is performed three times pernight in a
segmented lter with simultane-ous
u, g, r and i coverage. These
highairmass observations guarantee continu-ous monitoring of the
extinction, comple-menting the low-airmass Landolt eldobservations.
Other lters like Johnson B and V or Hα are
calibrated with Landoltstandards only if science data are takenin
these lters. Based on dedicated ditherobservations of the Landolt
elds in allchips and under photometric conditions,the OmegaCAM
consortium has builtup secondary standard star catalogues(currently
with more than 315 000 stars)in the key bands for the full 1 × 1
degreeeld of view.
Daytime calibrations consist of daily biasand dome ats, and
weekly gain/linearitymeasurements. Quality control duringthe day
focuses on monitoring the chipsensitivities, bias levels, dark
currentlevels, readout noise, gain and linearity,at lamp
intensities, twilight at levels,magnitude zeropoints and image
quality(FWHM and ellipticity). A descriptionof the OmegaCAM health
checks5 andthe resulting scores and plots6 is
main-tained. This follows the classic ESOapproach of scored health
checks main-tained by the QC group in Garching(Hanuschik et al.,
2008). An example ofthe detector-monitoring health check isshown in
Figure 7.
Challenges and outlook
VST operations have non-negligible over-heads, impacting
the completion progress
of the public surveys, which were plannedbefore the telescope
and camera per for-mance parameters were measured. Mostnotably, the
time used to bring and keep
the telescope focal plane to its bestshape is higher than
originally expected.In the rst two years of OmegaCAMoperations,
about 30% of the availablescience time was used for
acquisition,mainly image analysis. This can be com-pared to 10% for
VISTA. Related to this,OmegaCAM has a larger fraction of d
irectinteraction with the system for the tele-scope operator when
compared to VISTA.
Work is ongoing, in collaboration with theinstrument and
telescope consortia, toimprove the control procedures of
the VST main and secondar y mirrors, and tooptimise image
analysis algorithms onthe OmegaCAM side. The aim is to movecloser
towards fully automated opera-tions, including automatic
acquisition ofguide and image analysis stars.
Another area of improvement is the skyconcentration effect
that produces rota-tionally asymmetric features of 5% ampli-tude in
the sky ats (see the OmegaCAMuser manual7 ), and reection/scat
teringfeatures in images close to the Moon(within a few tens of
degrees). Calibratingout the sky at variations requires greatcare
in data reduction (see the consor-tium report on sky concentration
correc-tion7 ). Additional bafing for the VSTwill be tested at
the end of 2013; this willimprove the reproducibility of the
skyconcentrations in sky ats, and permitobservations closer to the
Moon, thusreducing idle time.
Survey progress and rst results
In Figure 8 the progress of the VST publicsurveys during the rst
two years of
operations is shown. In total, about 1000hours of observing time
per year havebeen spent on executing public surveyOBs within user
constraints.
Figure 7. An example of an O megaCAM heal th-check scoring
performed by the QC group in
ESO Garching. The left panel shows the dome atlevel averaged
over all 32 detectors, while the middlepanel shows the median level
for each detector. Thepanel on the right plots the score status of
eachdetector (labelled with their names: ESO_CCD_#65to ESO_CCD_#96)
as a function of time. If the domeat level falls below or exceeds
levels dened for eachdetector, then the square at that date will
tur n red.
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total KiDS/VIKING area of 1500 squaredegrees is about 40, with
> 10 above z = 6.5.
References
Baade, D. et al. 1999, The Messenger, 95, 15Bierwirth, T. et al.
2010, SPIE, 7737E, 19Capaccioli, M. & Schipani, P. 2011, The
Messenger,
146, 2Emerson, J. P. & Sutherland, W. 2010, SPIE,
7737E, 4Hanuschik, R. W. et al. 2008, SPIE, 7016E, 22Kuijken, K.
2002, The Messenger, 110, 15Kuijken, K. 2011, The Messenger, 146,
8
Venemans, B. et al. 2013, ApJ, 779, 24Wright, N. J. et al.
2013, MNRAS, in press,
arXiv:1309.4086
Links
1 ESO OmegaCAM webpage:
http://www.eso.org/ sci/facilities/paranal/instruments/omegacam
2 Setup and goals of the VST public
surveys:http://www.eso.org/sci/observing/PublicSurveys/ sciencePublicSurveys.html
3 ESO Phase 3
page:http://www.eso.org/sci/observing/phase3.html
4 Phase 2 P2PP software:
https://www.eso.org/sci/ observing/phase2/P2PP3.html
5 OmegaCAM quality control pages:
http://www.eso.org/observing/dfo/quality/OMEGACAM/qc/qc1.html
6 Health check scores and pl ots:
http://www.eso.org/observing/dfo/quality/OMEGACAM/common/ score_overview.html
7 OmegaCAM user manual and consortium repor t onsky
concentration correction:
http://www.eso.org/ sci/facilities/paranal/instruments/omegacam/doc /
In Figure 9, a few rst science resultsfrom VPHAS+ and KiDS,
kindly providedby the survey teams, are illustrated. In
the VPHAS+ example ( left), an ionised nebulasurrounding the
extreme red supergiant,W26, begins to be resolved (from Wrightet
al., 2013). As the only known exampleof a compact ionised nebula
around ared supergiant, this represents a unique
opportunity to study the mass loss of redsupergiants, using the
tools of nebulaastrophysics. The right panel shows oneexample of
the nine-band u to Ks photo-metry of KiDS (OmegaCAM) and
VIKING(VISTA Kilo-Degree Infrared GalaxySurvey) being used to hunt
for high-red-shift quasi-stellar object (QSO) candi-dates which
drop-out in the KiDS i -band(z > 5.7) and
VIKING z -band ( z > 6.5);from
Venemans et al. (2013). The histo-gram shows the redshift
distribution of allpublished quasars at z > 5.7
(in grey).Currently, more than 50 quasars at z >
5.7have been discovered in various surveys. The red histogram
bars show the redshiftdistribution of the quasars found in
thecombined KiDS/VIKING survey thus far. The number of quasars
expected in the
Telescopes and Instrumentation
Figure 8. Cumulative number of hours, since star t ofoperations,
spent on completed OBs for the three
VST OmegaCAM public su rveys . About 50–60% ofthe
available service mode time at VST is spent onpublic surveys. The
rest is shared between GTO andChilean programmes.
Figure 9. Left: A composite g-Hα- i image
of thedense, very massive cluster Westerlund 1, taken aspart of
VPHAS+, is shown. This image allows thestudy of the ionised nebula
surrounding the ex tremered supergiant, W26 (Wright et al., 2013).
Thezoomed part of the image (centre), shown in orange,is
Hα only. Right: High-redshift QSOs detected bycombining KiDS
(OmegaCAM) and VIKING (VISTA)data (Venemans et al., 2013),
indicated as red in thehistogram. See text for more details.
Right ascension06.2 4
2 . 0
3 8 . 0
3 4 . 0
– 4 5 : 5 0 : 3 0 . 0
D e c l i n a t i o n
2 6 . 0
05.8 05.4 16:47:05.0
Mieske S. et al., OmegaCAM Science Operations
http://www.eso.org/sci/facilities/paranal/instruments/omegacamhttp://www.eso.org/sci/facilities/paranal/instruments/omegacamhttp://www.eso.org/sci/observing/PublicSurveys/sciencePublicSurveys.htmlhttp://www.eso.org/sci/observing/PublicSurveys/sciencePublicSurveys.htmlhttp://www.eso.org/sci/observing/phase3.htmlhttps://www.eso.org/sci/observing/phase2/P2PP3.htmlhttps://www.eso.org/sci/observing/phase2/P2PP3.htmlhttp://www.eso.org/observing/dfo/quality/OMEGACAM/qc/qc1.htmlhttp://www.eso.org/observing/dfo/quality/OMEGACAM/qc/qc1.htmlhttp://www.eso.org/observing/dfo/quality/OMEGACAM/common/score_overview.htmlhttp://www.eso.org/observing/dfo/quality/OMEGACAM/common/score_overview.htmlhttp://www.eso.org/observing/dfo/quality/OMEGACAM/common/score_overview.htmlhttp://www.eso.org/sci/facilities/paranal/instruments/omegacam/dochttp://www.eso.org/sci/facilities/paranal/instruments/omegacam/dochttp://www.eso.org/sci/facilities/paranal/instruments/omegacam/dochttp://www.eso.org/sci/facilities/paranal/instruments/omegacam/dochttp://www.eso.org/observing/dfo/quality/OMEGACAM/common/score_overview.htmlhttp://www.eso.org/observing/dfo/quality/OMEGACAM/common/score_overview.htmlhttp://www.eso.org/observing/dfo/quality/OMEGACAM/common/score_overview.htmlhttp://www.eso.org/observing/dfo/quality/OMEGACAM/qc/qc1.htmlhttp://www.eso.org/observing/dfo/quality/OMEGACAM/qc/qc1.htmlhttps://www.eso.org/sci/observing/phase2/P2PP3.htmlhttps://www.eso.org/sci/observing/phase2/P2PP3.htmlhttp://www.eso.org/sci/observing/phase3.htmlhttp://www.eso.org/sci/observing/PublicSurveys/sciencePublicSurveys.htmlhttp://www.eso.org/sci/observing/PublicSurveys/sciencePublicSurveys.htmlhttp://www.eso.org/sci/facilities/paranal/instruments/omegacamhttp://www.eso.org/sci/facilities/paranal/instruments/omegacam
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E S O P
u b l i c S u r v e y s
The two VLT imaging survey telescopes: the Visi-
ble and Infrared Survey Telescope for Astronomy(VISTA, upper)
and the optical VLT Survey Tele-
scope (VST, lower).
E S O / G . H ü d e p o h l ( a t a c a m a p h o t o . c o m )
E S O / G . H ü d e p o h l ( a t a c a m a p h o t o . c o m )
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OmegaCAM (Kuijken, 2011). An overviewof OmegaCAM’s scientic
operations isgiven in Mieske et al. in this issue (p. 12). The
VST surveys are starting their thirdyear of operation. KiDS is the
largest sur-vey, requiring 3225 hrs to completion,or 39% of the
time, followed by 15% for VST ATLAS and 11% for VPHAS+.
Thetime allocated to Chilean programmes(10%), and Guaranteed Time
Observa-tions (GTO) of the OmegaCAM consor-tium (15%) and the
Italian National Insti-tute of Astrophysics (INAF; 10%) make upfor
a sizable fraction of the available tele-scope time, which has an
importantimpact on the speed of completion. Fig-ure 2 is a summary
pie chart of the timeallocation of the VST surveys as a per-centage
of the total available VST time forthe public surveys, Chilean and
GTO pro-grammes.
The rst spectroscopic public survey, theGaia–ESO survey,
started operation on
1 January 2012 on FLAMES at the VLTUnit Telescope 2 (Kueyen) on
Paranal. The data acquis ition for this survey is car-ried out
in visitor mode and the timeallocation of the survey entails 60
nightseach year, for an overall assignmentover four years
initially, with another yearpending a review of the survey
progressand delivered data. Thus far 105 nightshave been allocated
to the Gaia–ESOsurvey. The PESSTO survey started oper-ation on 1
April 2012, on EFOSC andSOFI at the New Technology Telescope(NTT)
on La Silla. The data acquisition forthis survey is also carried
out in visitormode. The time allocation for the surveyincludes 90
nights each year, with anallocation of 60/30 nights in odd andeven
periods respectively, for an overallassignment over four years,
also withanother year pending a successfulreview. Thus far 120
nights have beenallocated to this project.
Progress and estimated completion timefor imaging surveys
An integral par t of the approval of publ icsurvey
projects is the review of their sur-vey management plans (SMPs),
whichoutline the plans for telescope time allo-cation and observing
constraints overthe years. Additional information on qual-ity
control and pipeline data reduction,survey resource allocation for
the surveyexecution (full-time equivalent [FTE] allo-cation), the
timeline for the delivery andthe description of the data products
for
publication in the SAF are all part of theSMPs. Hence the SMPs
have becomethe benchmark that is used to computethe progress of the
public surveys andthey represent the basis for estimatingtheir
completion time. In service mode,the basic observation unit is the
observa-tion block (OB) and the time charged tothe programme is
accounted for in termsof the number of successfully completedOBs.
This includes the shutter open time(exposure time) and the relevant
over-heads provided in the execution timereporting module, which is
part of theobservation preparation software (P2PP3).
Successfully completed OBs are exe-cuted observations that full
the requestedobserving constraints according to strin-gent quality
control (QC) criteria that areexplained extensively elsewhere1.
Furtherinformation on the VST/OmegaCAM QCprocess, which was
designed followingthe QC for VISTA/ VIRCAM observations,is
given in the article by Mieske et al. (p.12). In the following, the
fraction of thecompletion for a survey is computed as afraction of
the total execution time inhours for the completed OBs normalisedby
the total time in hours requested inthe approved SMPs. The
cumulative dia-grams for the percentage of completionare shown in
Figures 3 and 4 for the VISTA and VST surveys,
respectively.
VISTA — The six VISTA surveys are pro-gressing at a
similar pace. As for anynew telescope the start of VISTA
opera-tions required some adjustments. After
Chilean
GTOOmegaCAM
GTO INAF
VST ATLAS VPHAS+
KiDS
Figure 2. Pie chart showing the time allocation
aspercentage of the total available time for the VST.
Figure 3. Graph of the percentage completion forthe VISTA
surveys as a function of date.
Figure 4. Graph of the percentage completion forthe VST
surveys as a function of date.
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asked to issue informed recommenda-tions on the continuation of
surveyprogrammes, or their termination, shouldthey consider any of
them not scienti-cally competitive at the time of the review.
Publication and download of sciencedata products from ESO public
surveys
The ESO policies in place to managethe public survey
projects monitor thedelivery of data products for ingestionand
publication via the SAF. Additionalallocation of telescope time is
conditionalon the submission of data products viaPhase 3. Phase 3
concludes the processstarted with the submission of the letterof
intent, followed by Phase 1 (proposalpreparation and submission)
and thepreparation and submission of OBs forobservations in service
mode, i.e.,Phase 2. As a result of Phase 3, the com-munity can
access and download thedata products from the SAF and is ableto
carry out independent science pro- jects in addition to those
targeted by thesurvey teams (c.f., Arnaboldi et al., 2011).
major technical interventions in 2010(camera shim installation
and horizontalre-centring) and 2011 (primary andsecondary mirror
recoating and extendedrecovery), operational procedures wereadopted
to increase the speed of execu-tion and reduce the number of
repeatedOBs. The current completion rate for the VVV and VHS
surveys is more than 67 %,while the percentage of completion is
inthe range 52% to 42 % for the other sur-veys (UltraVISTA, VIKING,
VIDEO and VMC).
VST — For the VST surveys, the per-centages of completion
are 66% for VST ATLAS, 22 % for KiDS and 38% for VPHAS+.
Of the three VST surveys, KiDShas the tightest requirements in
termsof Moon illumination (dark time) and see-ing constraints. It
is also, by far, the larg-est survey on the VST and thus, even ifit
uses a comparable fraction of time peryear to the other surveys,
its overall com-pletion is much smaller. Furthermore theright
ascension/declination distributionof the target elds overlaps with
those ofapproved GTO projects. Strategies arebeing implemented to
mitigate the com-petition, and speed up the data acquisi-tion for
KiDS, and also improve the over-all observation progress on the
VST.For more details see Mieske et al. (p. 12).
Taking account of the above percentagesof completion for
each survey and the
start of operation of each survey tele-scope, and assuming the
same observa-tion progress as previously, we can eval-uate the date
of completion for the VST
and VISTA surveys. Figures 5 and 6 showthe expected completion
time in yearsand the year of completion for the nineimaging
surveys. We expect the VVV, VHS and VST ATLAS to be completed
by2015, with the other surveys coming tocompletion in the following
years, withKiDS completed in 2021. For VHS, twonumbers are shown in
Figure 5: the com-pletion in 2015 is based on the 3400hours
requested in the SMP, but sincethe overheads were not known at
thetime of writing the SMP, this survey willactually need about two
years longer tocover the entire southern hemisphere, asshown by the
light blue bar. It is impor-tant to point out that these
projections donot automatically translate into telescopetime
allocated to these surveys. Theseestimates are upper limits since,
as onesurvey nishes, the others may progressfaster, which is not
explicitly taken intoaccount in the simple extrapolationabove. The
legacy value and the scienticexcellence of the survey programmesare
considered by the public survey pan-els organised by ESO and these
com-pletion dates are presented at major peerreviews. The public
survey panels are
ESO Public Surveys
Table 1. Summary of VISTA and VSTpublic survey products in
the ESOscience archive (Status: 25 October2013).
Survey
VHS
VIKING
VV V
VMC
Ultra-VISTA
VIDEO
ATLAS
VPHAS+
KIDS
Bands
YJHKs ZYJHKs ZYJHKs
YJKsYJHKsYJHKs
ugriz ugri, Hα
ugri
Sky coverage*
(sq.deg)
42102355643.61.81.8
234137556
Data volume
(GB)
8511288
2877268624
3015747701
Figure 5. Expected completion time, in years and byyear of
completion, for the VISTA surveys. For VHSthe time to completion
for the whole area coverageis indicated in light blue. T = 0 refers
to the star t ofscientic operations, i.e., April 2010.
Figure 6. Expected completion time, in years andby year of
completion, for the VST surveys. T = 0refers to the start of
scientic operations, i.e.,October 2011.
Arnaboldi M. et al., The ESO Publ ic Surveys
* The quoted sky coverage is the tota lgeometric area of
images, whichnormally differs from the nominal sur-vey area.
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The year 2013 has been very importantfor Phase 3
activities, as all eleven ESOpublic surveys submitted and
published
their data products via the SAF. The mile-stones for Phase 3
were the second VISTA submission for images and sourcelists,
and the rst submission for cata-
logues. The rst data release of the VSTsurveys was announced in
September2013. The spectroscopic public surveysare actively going
through the processof content validation and it is p lanned
thatthey will reach publication via the SAFby December 2013. Thus
far, a total vol-ume of 16 TB of data products —
images, weight maps, source lists andcatalogues — is now
available and full ysearchable via dedicated query inter-faces. In
Table 1 we provide an overview
of the data volume, wavelength andsky coverage of the data
releases fromthe imaging surveys. Further informationand detailed
descriptions of the datareleases from the ESO public surveys
areavailable2.
Public survey data are published throughthe ESO archive
interfaces conjointly withother products such as the stream forthe
ultraviolet and visual echelle spectro-graph (UVES) data that
results from thein-house generation of science dataproducts. All
Phase 3 data productscomply with the established standard forESO
science data products, therebyguaranteeing uniformity in terms of
dataformat and characterisation across theESO archive.
Figure 7 illustrates the current sky cover-age of the ESO survey
products in twoprojections. More than 4500 squaredegrees in the NIR
bands and 2400square degrees in the optical bands havebeen covered
by data products, whichare now accessible via the query inter-faces
of the SAF.
Merit parameters for ESO public surveysare the number of
refereed publicationsby ESO survey teams and archive users,the
number of press releases and thecumulative download of data
productsfrom the ESO archive. There are now71 refereed publications
from the surveyteams with a signicant increase in thenumber of
refereed publications (+200%)since November 2012, including
fromfour archive users, i.e., researchers whoare not members of the
survey teams. The contribution by Wegg & Gerhard(p. 54) is
an example of exciting scienticresults achieved using ESO archive
dataproducts (in this case from the VVV sur-vey). There also are
more than ten pressreleases based on VISTA data and morethan four
press releases for the VST.
The parameters on the data downloadby the community also
demonstrate astrong interest. The cumulative downloadfrom the SAF
since December 2011amounts to more than 6.8 TB of dataproducts and
~ 27 000 les. In Figures 8
and 9 these numbers are differentiatedper survey project and
data product type,respectively. The community is clearlyeager to
access the data, with the largest
Figure 7. Sky coverage of ESO public sur vey prod-ucts is
shown in two projections. Upper: Full sky(Hammer–Aitoff
projection); lower: Southern hemi-sphere (stereographic
projection).
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22 The Messenger 154 – December 2013
volume download coming from VVV,UltraVISTA and KiDS; see Figure
8. Thelargest volume download for products isfor the source lists,
followed by the tileimages. We believe that catalogues
willrepresent very valuable assets, as theyare the highest level
products for thesurveys. In this respect, we are workinghard to
reach a critical data volume soon,with the ingestion of the VIKING,
VVVand VMC catalogues so that the commu-nity can benet even more
from the jointeffort of ESO and the survey teams.
References
Arnaboldi, M. et al. 1998, The Messenger, 93,
30 Arnaboldi, M. et al. 2007, The Messenger, 127,
28 Arnaboldi, M. et al. 2011, The Messenger, 144, 17Emerson,
J., McPherson, A. & Sutherland, W. 2006,
The Messenger, 126, 41Kuijken, K. 2011, The Messenger,
146, 8
Links
1 Quality control
criteria:http://www.eso.org/sci/observing/phase2/ SMGuidelines/ConstraintsSet.VIRCAM.html
2 Phase 3 data releases: http://www.eso.org/sci/
observing/phase3/data_releases.html
ESO Public Surveys
Figure 9. Number ofles downloaded for thedifferent data
producttypes from the ESO SAFfor the public imagingsurveys.
Figure 8. Data volumedownload for the imag-ing public
surveys.
Arnaboldi M. et al., The ESO Publ ic Surveys
The 2.6-metre VLT Survey Telescop e (VST ) is show nin its
enclosure on Cerro Paranal. In the backgroundare the nearby VLT
Unit Telescopes 3 (Melipal, to theright) and 4 (Yepun, left).
http://www.eso.org/sci/observing/phase2/SMGuidelines/ConstraintsSet.VIRCAM.htmlhttp://www.eso.org/sci/observing/phase2/SMGuidelines/ConstraintsSet.VIRCAM.htmlhttp://www.eso.org/sci/observing/phase3/data_releases.htmlhttp://www.eso.org/sci/observing/phase3/data_releases.htmlhttp://www.eso.org/sci/observing/phase3/data_releases.htmlhttp://www.eso.org/sci/observing/phase3/data_releases.htmlhttp://www.eso.org/sci/observing/phase2/SMGuidelines/ConstraintsSet.VIRCAM.htmlhttp://www.eso.org/sci/observing/phase2/SMGuidelines/ConstraintsSet.VIRCAM.html
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23The Messenger 154 – December 2013
both at the VISTA Science Archive and atESO. Further details
about the VMC survey1 are given in Cioni et al. (2011).
Stellar populations
One of the main goals of the VMC survey isthe identication and
characterisation ofthe mixture of stellar populations that havemade
up the Magellanic system over time.
The star formation history of eld stars, thephysical
parameters of stellar clusters, thelinks between these and the
structure anddynamical processes are all embedded in the
VMC data. Ex tracting a comprehensive pic-ture of the
system represents our major chal-lenge, but fortunately we have
access tosophisticated tools with which to do the job.In Rubele et
al. (2012), we demonstrated thatby using two colour–magnitude
diagrams(CMDs) simultaneously, and a grid of modelsat various ages
and metallicities, we couldderive spatially resolved SFHs where
system-atic errors in the star formation rate and age–metallicity
relations are reduced by a factor oftwo, relative to previous work,
after account-ing for the geometry of the galaxy. In our studywe
independently derive the mean extinctionand distance modulus for
twelve subsectionsof the original tiles.
In Figure 1 we show the CMD of a tile in theSMC including the
Milky Way (MW) globularcluster 47 Tuc, highlighting the complexity
ofthe SFH analysis in decomposing the differentstellar populations.
Using custom-derivedpoint spread function photometry, we canpush
the sensitivit y of the VMC data to highlycrowded regions. Together
with the wide areacovered by VMC we will be able to investigatenot
only substructures in the LMC and SMC,but also streams at tached to
the 47 Tuc clus-ter, for example, as well as detecting themembers
of hundreds of stellar clusters in theMagellanic system waiting to
be characterised.
The reddening map of the 30 Doradus eld
Dust causes uncertainties in the measure-ments of the SFH and
the structure of galax-ies. Red clump stars (0.8–2 M and 1–10
Gyrold) are useful probes of interstellar reddeningbecause of their
large number and relativelyxed luminosity. Red clump stars
belongingto the tile LMC 6_6 are selected from theirlocation in the
( J–Ks) vs. Ks CMD. Then, theamount of total reddening
(along the l ine ofsight and within the LMC) in terms of
colourexcess is obtained for each of ~ 150 000 starswith respect to
its intrinsic colour. The latteris derived accordingly from stellar
evolution
Maria-Rosa L. Cioni1,2
Peter Anders3
Gemma Bagheri1
Kenji Bekki4
Gisella Clementini5
Jim Emerson6
Chris J. Evans7
Bi-Qing For4
Richard de Grijs8
Brad Gibson9
Léo Girardi10
Martin A. T. Groenewegen11
Roald Guandalini12
Marco Gullieuszik10
Valentin D. Ivanov13
Devika Kamath12
Marcella Marconi14
Jean-Baptiste Marquette15
Brent Miszalski16
Ben Moore17
Maria Ida Moretti14
Tatiana Muraveva5
Ralf Napiwotzki1
Joana M. Oliveira18
Andrés E. Piatti19
Vincenzo Ripepi14
Krista Romita20
Stefano Rubele10
Richard Sturm21
Ben Tatton18
Jacco Th. van Loon18
Mark I. Wilkinson22
Peter R. Wood23
Simone Zaggia10
1 University of Hertfordshi re, United Kingdom2
Leibniz-Institut für Astrophysik Potsdam,
Germany3 National Astronomical Observatory of
China, China4 ICRAR, University of Western Australia,
Australia5 INAF, Osservatorio Astronomico di
Bologna,
Italy6 Queen Mary University London, United
Kingdom7 Astronomy Technology Centre, Edinburgh,
United Kingdom8 Peking University, China9 University
of Central Lancashire, United
Kingdom10 INAF, Osservatorio Astronomico di Padova,
Italy11 Royal Observatory of Belgium, Belgium12
Institute of Astronomy, KU Leuven, Belgium13 ESO14
INAF, Osservatorio Astronomico di
Capodimonte, Italy15 Institut d’Astrophysique de Paris,
France16 South African Astronomical Observatory,
Cape Town, South Africa
17 University of Zurich, Switzerland18 Lennard-Jones
Laboratories, Keele Univer-
sity, United Kingdom19 Observatorio Astronómico,
Universidad
National de Córdoba, Argentina20 University of Florida,
USA 21 Max-Planck-Institut für extraterrestrische
Physik, Germany22 University of Leicester, United
Kingdom23 Australian National University, Australia
The VISTA near-infrared YJKs survey of the
Magellanic Clouds system (VMC) has
entered its core phase: about 50 % of the
observations across the Large and Small
Magellanic Clouds (LMC, SMC), the
Magellanic Bridge and Stream have already
been secured and the data are processed
and analysed regularly. The initial ana lyses,
concentrated on the rst two completed tiles
in the LMC (including 30 Doradus and the
South Ecliptic Pole), show the superior qual-
ity of the data. The photometric depth of
the VMC survey allows the derivation of the
star formation history (SFH) with unprece-
dented quality compared to previous wide-
area surveys, while reddening maps of high
angular resolution are constructed using
red clump stars. The multi-epoch Ks-band
data reveal tight period–luminosity relations
for variable stars and permit the measure-
ment of accurate proper motions of the stel-
lar populations. The VMC survey continues
to acquire data that will address many issues
in the eld of star and galaxy evolution.
The VMC survey
The VMC survey observations are obta inedwith the infrared
camera VIRCAM mounted on
VISTA and reach sta rs down to a limitingmagnitude of ~ 22
(5σ Vega) in the YJKs lters.
The VMC strategy involves repeated observa-tions of tiles
across the Magellanic system,where one tile covers approximately
uniformlyan area of ~ 1.5 square degrees in a givenband with three
epochs at Y and J, and 12epochs at Ks spread
over a time range of oneyear or longer. Individual Ks epochs
refereach to exposure times of 750 s and reach alimiting magnitude
of ~ 19 for sources withphotometric errors < 0.1 mag. The VMC
dataare acquired under homogeneous sky condi-tions, since
observations take place in servicemode, and their average quality
correspondsto a full width at half maximum < 1 arcsecond.
The VISTA astrometry, which is based on2MASS, results in
positional accuracies within25 milliarcseconds (mas) across a tile.
The
VMC data are reduced with the VISTA DataFlow System (VDFS)
pipeline and are archived
ESO Public Surveys
The VMC ESO Public Survey
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24 The Messenger 154 – December 2013
models, accounting for variations wi th ageand metallicity.
Extinction is subsequentlyconverted into hydrogen gas column
density.Compared to reddening maps producedusing the same method at
optical wave-lengths, the near-infrared VMC data are moresensitive
to higher extinction. Compared toH I observations we der ive
that, on average,half of the stars lie in front of the H
I columnand hydrogen becomes molecular in thedustiest clouds;
the transition begins atN H I ≅ 4 × 10
21 cm–2. Figure 2 shows thelocation of molecular clouds
superposed onthe distribution of hydrogen column densityinferred
from the VMC data. There is overallagreement with maps of dust
emission at24 μm and 70 μm (see Tatton et al., 2013).Reddening maps
will be created for other tilesin the VMC survey allowing red clump
starsto be de-reddened; these results will be usedin calculating
the three-dimensional (3D) struc-ture of the Magellanic system.
Variab le stars
The other main goal of the VMC survey isthe measurement of
the 3D structure of theMagellanic system. Classical Cepheids
areprimary distance indicators and in the near-infrared obey
period–luminosity (PL) relations
that are less affected by reddening, chemicalcomposition and
nonlinearity than those atoptical wavelengths, resulting in smaller
intrin-sic dispersion. First results for classicalCepheids in the
tiles LMC 6_6 (Figure 3, left)and 8_8 have been presented in Ripepi
et al.(2012). The identication of the variab les isderived from the
EROS-2 and OGLE-III cata-logues and their VMC Ks light curves
are verywell sampled, with at least 12 epochs, andhigh precision,
with typical errors of 0.01 mag,or better, for individual phase
points. The Ks mag of the faintest Cepheids in the LMC,which
are mostly rst over tone pulsators, wasmeasured for the rst time
thanks to the
VMC observing strategy. Photometr y for thebrightest
fundamental mode Cepheids (peri-ods > 23 days), exceeding the
linearit y regimeof VMC data, are taken from the literature.
Thedispersion of the PL relations is ~ 0.07 mag.
Anomalous Cepheids (1.3–2.1 M and
[Fe/H] ≈ –1.7 dex) also play an impor tant roleboth as distance
indicators and stellar popula-tion tracers. The VMC survey has
alreadyobserved many of the anomalous Cepheidsdiscovered by the
OGLE project in the LMC.
These stars obey a tight PL relation in theKs-band with a
dispersion of 0.10 mag (Fig-ure 3, right) that is shown for the rst
time inRipepi et al. (2013).
Cepheids (< 200 Myr old) are mainly concen-trated towards the
bar and in a nor thwest
spiral arm of the LMC as well as in the centralregion of the
SMC. Eclipsing binaries com-posed of main sequence stars trace a
simi lardistribution, but with clustering mainly occur-ring in
regions of recent star formation. Onthe other hand, RR Lyrae
variable stars(> 10 Gyr old) are smoothly distributed andlikely
trace the haloes of the galaxies. Thesestars also follow a PL
relation that is tightin the Ks-band. The VMC properties and
thestrategy to measure distances and infer thesystem 3D geometry of
different age compo-nents from the variable stars is described
inMoretti et al. (2013).
The magnitude of the brightest VMC objects(10 <
Ks < 12), which may be saturated in theircentral regions,
is well recovered by the VDFSpipeline by integrating the ux in the
outerparts. Most of these sources are asymptoticgiant branch (AGB)
stars. By tting spectralenergy distributions, created from the
combi-nation of VMC data and data at other wave-lengths, with dust
radiative transfer models, itis possible to derive mass-loss rates,
luminosi-ties and spectral classications that offerstrong
constraints on AGB evolutionary mod-els (Gullieusz ik et al.,
2012). These variablestars obey PL relations that may also be
usefulas distance and structure indicators.
The proper motion of the LMC
The astrometric accuracy and the photometricsensitivity of
observations made with VISTAare of sufcient quality to select a
large sam-ple of targets and measure their proper motion.
The proper motion of the LMC is measuredfrom the
combination of 2MASS and VMCdata that span a time range of ~ 10
years andfrom VMC data alone across a time baselineof ~ 1 year
(Cioni et al., 2013b). Dif ferent typesof LMC stars (e.g., red
giant branch, red clumpand main sequence stars, as well as
variablestars) are selected from their location in the( J–Ks)
vs. Ks CMD, and from lists of knownobjects, where MW
foreground stars and back-ground galaxies are also easily
distinguished(Figure 4, left). The proper motion of ~ 40 000LMC
stars in the tile, with respect to ~ 8000background galaxies, is
μαcos(δ ) = +2.20 ±0.06 mas yr –1 and μδ = 1.70 ±
0.06 mas yr
–1. This value is in exce llent agreement wi th previ-ous
ground-based measurements but ourstatistical uncer tainties are a
factor of threesmaller and are directly comparable to
uncer-tainties derived wi th the Hubble Space Tele-scope. The error
budget is at present domi-nated by systematic uncertainties (a few
masyr –1), but these will decrease due to theimproved reduction of
the VISTA data and theincrease in the time baseline.
ESO Public Surveys
Figure 1. Colour–magnitude diagram of stellarsources in tile SMC
5_2. All sources are shown ingrey; stars belonging to the SMC
cluster NGC 121are indicated in blue; the eld population of theSMC
is indicated with yellow contours; and the starsof the Milky Way
cluster 47 Tuc are shown with red
contours.
Figure 2. Hydrogen column density map inferredfrom VMC data in
tile LMC 6_6 identifying regionswhere N H I > 8 ×
10
21 cm–2. Crosses representmolecular clouds catalogued in
the literature andellipses highlight those with measured
properties.
Cioni M.-R. L. et al., The VMC ESO Public Survey
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formation of the Bridge and the existence ofstripped stars. The
VMC survey has a high leg-acy value and represents the sole
counterpartin the Ks-band to current and future ground-based (STEP
at the VST, SkyMapper, SMASHat the Blanco 4-metre, Large Synoptic
Survey
Telescope [LSST]) and space-based imagingmissions (e.g.,
Gaia and Euclid) targeting orincluding the Magellanic system. It
also pro-vides a wealth of targets for wide-eld spectro-scopic
follow-up investigations, e.g., with the
Apache Point Observatory Galactic EvolutionExperiment
(APOGEE)-South, High Efciencyand Resolution Multi-Element
Spectrograph(HERMES) at the Anglo-Australian Observatory,4-metre
Multi-Object Spectroscopic Telescope(4MOST) and Multi-Object
Optical and Near-infrared Spectrograph (MOONS) at ESO.
Refer