H-band multi-object spectroscopy around the Galaxy

March 22, 2010 Science with the William Herschel Telescope 2010-2022

H-band multi-objectspectroscopy around the Galaxy

Carlos Allende Prieto (IAC)

and the APOGEE Team


APOGEE

• A high-resolution (R~30,000) high-S/N

H-band spectroscopic survey of 100,000 stars in the Galaxy

• Why high-resolution? Why in the H-band? Why now?


Rationale

• Red giants/red clump have strong NIR flux. Complete point source sky catalogue to H ~ 13.5 available

from 2MASS• AH / AV = 0.17 (x 100 in flux at AV ~6) • Access to dust-obscured galaxy • Velocities to <1 km/s accuracy and precision abundances (15 elements) for giants across the Galaxy• Low atmospheric extinction makes bulge declinations

accessible from North (though over smaller field)• Avoids thermal background problems of even longer


APOGEE Science Case

• In the context of Galaxy structure and evolution: sampling the distribution functions (x, v, Z) of the Milky Way avoiding the biases of working at visible wavelengths

• In a broader context: does the Milky Way fit in a -CDM universe?


Terra incognita

• Local thin disk well studied (Geneva-Copenhagen, S4N, Fuhrmann papers …)

• Local and more distant halo well studied (SDSS)

• Local thick-disk well-studied (just recently)• Not the case for the bulge (only Baade’s

window explored) or distant parts of the Galactic disk


Specific objectives• Disk/Rotation Curve

Surveys of stellar disk dynamics outside solar vicinity typically <~100 starsHI tangent point analyses assume circular rotationinsensitive to non-axisymmetric effects (e.g., arms) andinoperable outside solar circle [V(>Rsun) poorly known]s I

Gradients/lack of gradients in the thin/thick disks o Gas/stars in the spiral arms

• Galactic Bar• Little current data, but possibly wide-ranging influence. Radial

motions affect gas-mixing, metallicity gradients• Bulge

Poorly known. Connection of velocities and chemistry provide s strong constraints on inflow of material into bulgear

• Halo• Internal dynamics of substructure. Inner/outer halo dichotomy


What makes APOGEE’s spectrograph unique?

• We know: Phoenix (KPNO 2.1m,4.1m, CTIO 4m, Gemini South), NIRSPEC (Keck), CRIRES (VLT)

• We heard of NAHUAL (GTC), CARMENES (3.5m CAHA)

R range detectorPhoenix 50,000-80,000 1-5 m 0.5x1 K

CRIRES <100,000 0.95-5.2 4x0.5x1K

NIRSPEC 25,000 (2,000) 0.95-5.5 1x1 K


What makes APOGEE’s spectrograph unique?

• Focused in the H band• Larger detectors• Grating (VPH vs. echelle): spectral coverage, efficiency• Multi-object (300 fibers)

APOGEE 30,000 1.5-1.7 3x2x2 K

Phoenix 50,000-80,000 1-5 0.5x1 K

CRIRES <100,000 0.95-5.2 4x0.5x1K

NIRSPEC 25,000 (2,000) 0.95-5.5 1x1 K


Hardware Overview

Camera

VPHgrating

Fibers in & LN-2 autofill

Collimator

Fold 2 (dichroic)

Fold 1

Detector Assembly (mounts to Camera)

Fiber RacetrackSlithead

(fiber “launch”)


Hardware overview(Univ. of Virginia)

• Fibers (high-transmission low frd): 40 m H-band optimized (65% throughput). Prototypes near top expectations in hand

• Design includes a dichroic (cutting out thermal IR)

Thanks to Fred Hearty for passing all the info!


Collimator


VPH

• Size matters. Design calls for a 50x30 cm grating!

• 3 recorded panels on a single gelatin substrate, sandwiched by two

2.5-cm layers.

Several prototypes have

demonstrated feasibility

(should be done in April)


Volume Phase Holographic (VPH) Grating


Camera• All lenses

built and coated

assembly to

begin in two

weeks

• 3 Teledyne

2048x2048

detectors

(same as for JWST)

QE~85% (dithering capabilities!)


Camera


Camera


Cryostat

• All spectrograph cooled to 80 K in vacuum• No entrance window• Cryostat is 2.5x1.5x1.5m• Vibration isolated with common commercial

solutions (>99% removed at >10 Hz)• Active thermal control (~1e-3 K)• Multiple calib. Sources (ThAr, U, laser comb)• Cryostat had 1st vacuum test, ready for 1st cold

test. Delivery should happen in April





Deliveries• A rich window sampling 15+ Elements (including C,N,O)• R~30,000 provides<<1 km/s velocity errors(probably much much smaller, but stellar jitter)• Fully automated reduction + analysis pipeline• 300 fibers on, 1e5 stars using bright time 3 yrs on ARC 2.5m


WHT• An APOGEE-like spectrograph on WHT would be

a different instrument: smaller field, different science (e.g. clusters, extra-galactic red giants, integrated extragalactic globular clusters)

• APOGEE, the spectrograph, costs is estimated at ~ 7 M$ (but much cheaper to repeat!)• Concept fully proven• Pipeline/acquis. Software can be recycled• IAC is negotiating full participation in SDSS-III

(i.e. in APOGEE)


Another interesting example …VIRUS on the HET

H-band multi-object spectroscopy around the Galaxy

Documents

apogees spectrograph

distant halo

5x1 kcrireswhat

provideswhtan apogee

milky way

apogee science casein

studied genevacopenhagen

context of galaxy structure