[email protected] Observational Astrophysics II: May-June, 20051 Observational Astrophysics II (L2)

Observational Astrophysics II: May-June, 2005 [email protected]

Observational Astrophysics II (L2)

http://www.astro.su.se/utbildning/kurser/astro_obs2/


Observational Astrophysics II (L2)

Getting our NIRF

What do we want to do?

1. Image a selected spiral galaxy in H6563 (HII/slit position)2. Spectroscopy of HII regions => los radial velocities3. Imaging in JHK => isophotes => deprojection => Vrad(r) => rotation curve and => stellar population from colours


Spectrograph Slit

Radial Distance, r (arcsec to kpc)

Error Bars ???!

VGalaxy


The Spiral Galaxy M83

in broad band R in narrow band H

H II regions – point likeStellar pop - extended


H line-to-continuum contrast In

narrow band filter

continuum

U B V R I


Example of

long-slit observation

(spatio-spectral mapping)

1´´ wide 2´ long

spectrograph slit

star

supersonic

jet flow


K-s

pe

ctrum

of S

erp

ens

SM

M1

jet (VL

T-IS

AA

C)

rovibrational H2 lines

Sp

atia

l Do

ma

in

Spectral Domain 1´´ slit

star

2´

slit

S(3) =2-1S(2) =2-1

R = 400


R = 400(v = 750 km s-1)

R = 100 000(v = 3 km s-1)

Radial velocity measurement


Observing our galaxies1. ALFOSC H imaging

What Filter?

= 6563 (z + 1) Å

z (Å)

10-4 0

10-3 6570

10-2 6630

10-1 7220

http://www.not.iac.es/instruments/instruments.html


Observing our galaxies2. ALFOSC H spectroscopy

What slit width?


ALFOSC Slits The following slits are available for use with ALFOSC:

Simple, long-slit, covering the full spatial field of view of the instrument (in arcsec):

0.4, 0.5, 0.75, 1.0, 1.2, 1.3, 1.8, 2.5, 5.0, 10.0

Long-slit spectra are oriented vertically on the detector. The 1.8" slit is not very smooth and shows considerable flux variations along the slit.



What spectral resolution?


Sun at 8.5 kpc 250 km s -

1

= v/c R = v (km s-1) (Å) R

30 0.65 10000

300 6.5 1000

3000 65 100

30000 > 650 < 10



What integration times?

1. NOT (or ESO) Exposure Time Calculator

http://www.not.iac.es/observing/forms/signal/


Exposure Time Calculator

• Instrument ALFOSC Spectroscopy• Detector CCD8 (CCD7)• Grism http://www.not.iac.es/instruments/alfosc/grisms/• Band• Bandwidth• Slitwidth• Source Extended• Mag• FWHM • Exptime• Airmass• Extinction http://www.ast.cam.ac.uk/~dwe/SRF/camc_extinction.html• Sky Brightness B



What integration times?

2. Manual Estimate

ronbgsource

2source

)(

)(

ntnn

tn

N

S

Quantify the ns . . .[ for t =1s and t ~ (S/N) 2 ]


source

aha...

IS transport

diffraction

electronics

Obs. analysis: Reduction Calibration Informatics

telluric atmospheric

transport-turbulence

sphericalcoherent - incoherent

cow

coherent – incoherent

detection

Plane Wave

Two Domains:

Above & Below

Atmosphere


1. Above telluric atmosphere

Photons gained

Source direct emission scattered into beam

Extra-Galactic BackgroundGalactic BackgroundZodiacal Background

Photons lost

Source direct abs/extinction scattered out of beam

Extra-Galactic ExtinctionGalactic Extinction (IS)Zodiacal Extinction

A good emitter is also a good absorber (Kirchoff’s law)


2. Below telluric atmosphere

Atmosphere emission extinction scatteringOptics emission absorptionDetector absorption emission

Transmission, T

Extinction,

Efficiency,

Detector Noise


Collecting terms:

1. Signal degradationAtmosphere transmission Tatm (%)Telescope reflectivity Ttel (%)Filter transmission Tfilter (%)Spectrograph throughput Tspec (%)Detector efficiency QE (%)

2. Noise sourcesSource Photons Poisson

Background Photons Sky + Telescope

Detector emission Thermal or Dark Current Detector Read Noise Read out noise


)90cos(

1sec:airmass

)101(

d :S

secatm

specfilsecprimatmdetctor

source

hz

T

FTTTTTF

z

Ω

D

ΩIF

T

T

T

iT

hz

eT

AT

FTTTTTTF

nconvolutio

i

i

z

A

i

angle solid a subtending

and distanceat source a from atmosphere sEarth'

theabovedensity flux corrected extinction theis d

] 1.0 [hput aph througsprectrogr theis

] 1.0 [nsmission filter tra sorting,order e.g. the,is

] 1.0 [ seeing e.g. todue losses,slit for acccounts

0.98] 0.99 [ etc.)secondary (primary, mirror ofty reflectivi theis

)90cos(

1sec is Airmass theand

tcoefficienion extintinct catmospheri ,

extinction IS of magnitudesin , 10

d )(

:integral aby given isdetector theontoflux photon Source

0

spec

filt

slit

2

M

secatm

4.0ext is

0specfiltslitMatmext isdet


Signal = Source flux Ftel for given V, E(B-V)

11source

pixelsource

source

1sÅ

erg

1Å2cm1s erg1

2cm)sourcedim(:checkdim

1-V12

eff

telV

telsource

1210V

sectelV

121V4.0)(1.34.090V

VV

12190Veff

04.0

pxl s xel)](arcsec/pi scale image[

then,´´1 of image limited seeingand/or slit torefers if

s Å) 827 ()erg1065.3/(

~

detector onto secper photons source ofNumber

Åcms erg

Åcms erg 10101067.3

)(1.3)(

Åcms erg1067.3 ,Å5483for where, 10

eff

V

V

-

----n

j

j

---z

---VBE

---mmm

nn

n

hc

FTSn

FeF

F

VBEVBERA

FFF

Similar can be done at any other filter wavelength, e.g. in the R band


Sky Backgrounds are generally given in mag/arcsec2 (surface intensity) and are treated similar to source fluxes

Dark current and read-out-noise are device specific normally provided externally (manufacturer/observatory)

ALFOSC CCD # 8

2048 x 2048 13.5 m pixelsimage scale 0.19´´/pxl

dark current 0.4 e- / pxl / hr

ron 5.3 e- / pxl (read time 90 s)

conversion* 0.765 e- / ADU (high gain)well capacity 63 000 ADU (~216, high gain)non-linearity 0.3 %QEV 0.75

* Analogue-to-Digital Unit


Worked example: NOT-ALFOSC H image

Galaxy R = 13 mag E(B-V) = 0.02 magR = 0.02 Airmass = 2 Seeing = 1´´ filter #49 = 50 Å eff = 6607 ÅLine-to-continuum = 1 Sky background = 18 mag


nintegratio of 1secin

6

24

2

11sky

skysky

11H

12eff

121140R

H2

telsource

121142020134.0031.04.09telR

VR

12190Reff

40~1717

107.2

93.61)1045.1252200(75.0

)1220075.0(

pxl s ADU 25~

mag 18~mag 3~Moon Full

pxl s ADU 2200 /ADU)e (0.765 /pxl)´´19.0( Å) 50 (

)erg1003.3/(

)Åcms erg101.14()76.0()cm 25.62250(~

Åcms erg101.14e 10101092.1

031.002.01.38.0)(8.0~

Åcms erg1092.1 ,Å6855 R

N

S

n

RR

hc

FTSn

F

VBERA

F

-

--

----

----.-

---m

Worked example: NOT-ALFOSC H image, ctnd.

Normally, one makes the computation in electrons and converts at the end.However, at the telescope, the student should watch the ADUs (linearity check).


Obs. Group

Filter (type / #)

Grism

#

Slit(arcsec)

Object(Name)

RA 2000

(h m s)

Dec 2000

(o ´ ´´)

Proposal

.and.

Finder chart (Y/N)

1Katarina

Åsa

22, 78, 49

8, 5, 7 0.75, 1.0, 1.3, 2.5

5.0

NGC 5112 13 21 56.43 38 44 04.6 Y

2Kristoffer

Sven-Ingmar

78 8 0.5, 0.75, 1.0, 1.2

NGC 5879 15 09 46.82 57 00 02.6 Y

3Michael

Kristina

77, 50, 49,

68

8, 5, 7, 4, 3

5.0, 2.5, 1.0, 0.5,

1.2

NGC 6389 17 32 39,77 16 24 06.4

ALFOSC admits MAX check thickness!!! 7 Filters: UBVRI +2 12 FASU: 6 Grisms: 5 Slits:


Preparing our NIRF

http://www.not.iac.es/observing/guide/#preparation

http://www.not.iac.es/observing/cookbook

Before we go to the mountain...

[email protected] Observational Astrophysics II: May-June, 20051 Observational Astrophysics II (L2)

Documents

observational astrophysics

v galaxy slide

alfosc h spectroscopy

narrow band h h

v rad r

alfosc h imaging

l2 http

r arcsec