Download IR Spectroscopy

IR Photometry
Spectroscopy
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Crudest resolution : photometry
 spectral energy distribution (SED)
U(0.37), B(0.44), V(0.55), R(0.64),
Gound-based IR : I(0.80), J(1.25),
H(1.65), K(2.2), L(3.5), M(4.8), N(10),
Q(20 mm)
 12, 25, 60, and 100 mm IRAS bands
 Dl/l ~< 0.01 :  spectroscopy
Ground-based IR Photometry
 Two regimes :
 JHKLM : shorter (sensitivity range of
InSb detectors)
 NQ : longer (covered by bolometers
and various photoconductive or
photovoltaic detectors cooled to < 10
K)
 JHKLMNQ ; corresponds to a clear
“window” of atmospheric transmission
Window of Atm & Photometric
bands, J. H, & K
 Johnson(1965) and Kitt Peak filters
Window of Atm & Photometric
band L
 Simons(1996)
Window of Atm & Photometric
band, M
 Simons(1996)
Window of Atm & Photometric
bands, N & Q
 Tokunaga(1999)
Window of Atm & Photometric
band, Q
 Simon et al(1972
IR Photometry
 Magnitude :
 ml =-2.5 log R +ZP ,
R= the instrumental response in the band,
ZP = constant, zero-point
 Vega (bright A0V star) : zero mag at all wavelengths
  the average of (V- ml) for all A0V stars is zero for
all bands
 Johnson et al(1966) : Vega at JHK =0.02 at each
wavelength (also posses a circumstellar dust shell –
beyond 20mm ;unsuitable for use as a standard at
longer l )
Effective Wavelength
 Effective wavelength of a filter :
 leff = ∫ l S(l) h(l) dl / ∫ S(l)h(l) dl
 S(l) : transmission of the filter
 h(l) ; quantum efficiency of the
detector
Derivation of monochromatic
flux densities from photometry
 The calibration of a standard star system
is given as the flux corresponding to a
zero mag star at the effective l of each
band
 Because of the difficulties associated
with conversion of mag. Into absolutely
calibrated monochromatic fluxes, choose
to discuss colors and magnitudes.
Flux Correction Factor k
 Can construct correction tables for various
assumed intrinsic spectral energy distributions
with paticular filter transmission curves ,
the correction factor k, such that
Fltrue(leff) = Flapparent (leff)/k
for a particular monochromatic flux density
distribution Fl(l) ,
can be calculated as follows :
k={∫ Fl(l) S(l) dl / Fl(leff) } / {∫ Flstd(l) S(l) dl
/ Flstd(leff)}
Factor k calculated for BB
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T
5000
3000
1000
800
600
400
300
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Standard star is assumed to have a 10000 K BB spectral energy distribution . The
detectors were modelled as a photon detector with responsivity proportional to l for JHKL
and a bolometer for N. The JHKL filters were taken to be those of the SAAO(Carter, 1990)
system with a hypothetical N- band from 8 to 14 mm. The precise values of the k-factors
will differ from on photometric system to another
kJ
0.99
0.96
1.03
1.14
1.42
2.62
5.48
kH
1.00
0.98
0.98
1.01
1.09
1.44
2.10
kK
1.00
0.99
0.98
0.98
1.00
1.09
1.25
kL
kN
1.00 0.99
0.99 0.99
0.98 0.95
0.97 0.94
0.97 0.92
0.99 0.90
1.04 0.92
Isophotal wavelengths
 To find the l at which the simply-derived value for
Fl is the correct one.
 The Isophotal wavelength of a filter and star
combination is to be that quantity li which satisfies
the relation
 Fl(li) ∫ S(l) dl = ∫ Fl S(l) dl = R
 Fl(l) is the monochromatic flux density from the
star in units of W m-2sec-1mm-1, S(l) is the
efficiency of the photometric system. R is
proprotional to the response of the system( eg, the
output voltage of the detector)
IR Photometric bands
 Main problem ; the interference filters
that define the bandpass cannot be
reproduced with perfect accuracy
 Solve  Having all filters in made the
same batch manufacturing process
and by observing the same set of
standard stars.
JHKLM
 Johnson(1962) : K (2.2mm) and
L(3.6mm)
 Johnson (1964) : J (1.20 mm), K (2.20
mm) L (3.5 mm) and M(5.0 mm)
 Johnson et al 1968 : H (1.65 mm)
 Photovoltaic InSb  L’ (3.8 mm)
 Ks (2.0-2.3 mm), K’ (1.9-2.3 mm)
Window of Atm & Photometric
bands, J. H, & K
 Johnson(1965) and Kitt Peak filters
Window of Atm & Photometric
band L
 Simons(1996)
Window of Atm & Photometric
band, M
 Simons(1996)
Narrow-band CO and H2O
photometry
 Sub-band of the K-band to isolate
regions affected by CO (a narrow band
filter centered at 2.36 mm) and water
vapor( at 2.00 mm)
 A third narrow-band filter around 2.20
mm used for to define the unaffected
continuum
MIR, ground-based photometry
 Ge-doped bolometers, Doped Si arrays
N-band (8 – 14 mm) :
SAAO (1982) : cutoff 7.7mm , 80% to ~ 14 mm
Rieke et al (1985) at 10 and 20 mm
Thomas et al (1973) : narrower bands centered at 8.4
and 11.2 with broad-band N at 10.2 mm
 ESO : three narrow bands N1(8.4) , N2(9.69) and
N3(12.9)
 Low and Rieke (1974) : bands at 11.5 and 13 mm
 Young et al (1994) ; narrow bands at 9.0 and 11.0 mm
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Q band region (17-27 mm)
 Poorly defined
Standard Star Observations
 SAAO standard program of
Carter(1990)
 Observing dwarf stars around A0 to set
zero colors of V-K, J-H, H-K, and KL for dwarfs with B-V=0
 Bessell and Brett (1988) ; set Vega’s
all color zero.
JHKL standard star programs
 Johnson (1964) ; adequate for a decade, not extend to the
southern hemisphere
  Glass (1974) in Cape Town,
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Carter (1990) at Sutherland (SAAO),
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Engels et al (1981) and Bouchet et al (1991) at La Silla
(ESO)
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Allen and Cragg (1983) at the Anglo-Australian
Observatory (AAO)
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Elias et al (1982, 1983) at Caltech and Cerro Tololo
 Jones and Hyland (1982) & McGreger (1994) at Mount
Stromlo (MSSSO)
Faint standards
 UKIRT and related standards : a set of
faint standards (8 < K < 14 mg) ;
transformation eq to the CTIO-Caltech
system (Casali and hawarden 1992) &
extended by (Hunt et al 1998)
 Persson et al (1998) : 65 faint (10 < K
< 12 )stars : J, H, K and Ks
Intrinsic colors of dwarfs
 Besell and Brett(1988)
Influence of molecular
absorption on broad band
colors
 Deviation of Giants in J-H, and H-K
from the locus of BB : max at M2-M3
giants : due to the min. of the
continuous b-f, f-f apsorption of H At < 3250 (M6) ;effect of H2O begin to
dominate
 M-band at 4.8 mm strongly affected
by CO  L-M of giants < 0 at late M
Color-color
 Dependance of J-K on metallicity
 d (J-K) ~ 0.15 for d (Z/Zo) = 1.5 : J-K becomes bluer for low metallicity
 Deviation from BB increases for low metallicities
Absolute calibration
 I. Solar method :
1. observe G2 V stars’ V-J, V-K, V-L
2. take Vo= -26.74 . Derive apparent JKL mags of the sun
3. absolute energy distribution of the solar radiation taken from
Allen(1963)
 II. BB comparision method :
Walker (1969) 1.06, 1.13, 1.63 and 2.21 mm (detector PbS cell
cooled to dry ice T) ; overall accuracy 10%, Selby et al (1983) narrower
bands +-4%
 III. Comparison with stellar models :
Cohen et al (1992) models of Vega and Sirius by Kurucz, normalized
at measurements at 5556A, and use them to calculate isophotal
wavelengths and monochromatic flux densities for various photometric
systems.
Absolute calibration
 Bessell, Castelli and Plez (1998)
IRAS Photometry
 Van der Veen and Habing(1988)
Bolometric Mag.
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apparent bolometric mag
mbol = - 2.5 log ∫ Fl dl + C
C = -18.980 in W m-2,
-11.480 in erg cm-2 s-1
Absolute bolometric mag
Mbol =4.74 -2.5 log (L/Lo) for solar
constant 1360 W m-2
 Lo = (3.826 +-0.008) * 1026 W
Stellar effective Temperatures
F = (f/2)2 s T4eff
F ; tatal observed flux
f : observed angular diameter
Ridgway (1980) : spectral type vs
T eff, V-K , and I(104)-L colors
Di Benedetto (1993) ; tables of
BC and Teff for stars of 1.42
< (V-K)o < 7.60 and luminosity
classes I-V
Infrared Flux method
 To get Teff : Blackwell and Shallis (1977) : a measurement of
a star’s bolometric mag and a single near-IR continuum
point  determine Teff of it
 Megessier (1994) : shows ratio R =sT4 /Fl is sensitive to
metallicity effect and gravity, besides temperature.
  the metallic lines reduce the UV flux, causing more energy
to IR for a given effective T; order of 1 % Teff,
 different gravity may change it by half
  order 2%
JHKL photometry of galaxies
 Galss (1984) : average colors of ordinary nearby galaxies
Poggianti (1997) : k correction (changes of wavelength, bandwidth and
intensity associated with reshift) in i filter
 Ki = -2.5 log (1+z) + 2.5 log ((∫ Fl (l) S(l) dl )/ (∫ Fl (l/(1+z)) S(l) dl))
 S(l) : response of the filter and photometric system, z = red shift
F(l) : observed flux density from the galaxy
 1st term : arises from the narrowing of the filter passband in the restframe of the galaxy by a factor (1+z)
 2nd term : allows for the fact that radiation seen by the observer at
k-correction for galaxy
photometry
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Typical K-corrections
J-K -0.5z
H-K -3.5z
K
3.3z
 These quantities must be added to the observed quantity to get
the rest-frame quantity : Frogel et al (1978)
 Approximately linear up to z=v/c = 0.2
 Comprehensive tabel of K-correction :
Poggianti(1997)
K-correction
 Remember : a power law spectral distributiion
undergoes Lorentz transformation without
change of spectral index, and a BB spectral
distribution transforms to another BB distribution ,
but with lower T.
  observed T
 Tobs =T(1-b cos q) (1-b2) -1/2
 q : direcction of the motion to the line of sight
 b = v/c
Photometric determination of
redshifts
 Use of multicolor photometry
 Connolly et al (1995) ; galaxies out to z~0.8 and
Bj < 22.5 using filters similar to the standard
UBRI
 4000 A break : cease to be useful ~ z=1 (it
passes beyond I band)
 Work well for z> 2.2, where the Lyman limit(912A)
enters the U-band
 Connolly et al(1997) : including J band to solve
the problem of determining z for 1<z< 2
Effects of Star formation
 Colors of a galaxy bluer due to the
presence of many hot, young stars.
 Galaxy evolution model : Leitherer et al
(1996)
 Ellis 1997: star fomation peak ~ z=2
 The slope of the relation between K
mag and log (# of galaxies deg-2
mag-1) begin to turn over at K~ 19
Modelling galaxy Evolution
 Stellar populations : generated either
initially, or contunously, according to
certain conditions, such as metallicity,
and mass function.
Galaxy colors at high redshift
 Observed color of galaxies at high
redshift : function of both evolution
and redshift.
 Mobsher et al (1993) : at K band
 E/S0 and spiral galgxies have identical
luminosity functions ;peak at K ~ 19
 Star formation : Max at z =2
Homework
 The color indices of main sequence stars are given
in the table. Find the colour temperature of the
various spectral types (that is the temperature of the
BB with the most similar spectrum in a given
wavelength interval). For simplicity, represent each
band by its central wavelength.
Presentation 2
 ESO Symposia: High Resolution Infrared Spectroscopy in
Astronomy, 2005. © Springer-Verlag Berlin Heidelberg 2005
 Spectral Properties of Brown Dwarfs and Hot Jupiters Derek
Homeier et al ; p 465
 Near-Infrared Spectroscopy of Deeply Embedded, Young
Massive Stars Lex Kaper and Arjan Bik : p143
 R=100,000 Mid-IR Spectroscopy of UCHII Regions: High
Resolution is Worth it! Daniel. T. Jaffe : p 162
 Outflows in Regions of Star Formation Ren´e Liseau : p185
 High-Resolution Infrared Spectroscopy of Protoplanetary Disks
John S. Carr : p 203
 Active Stars and He I 10830 ˚A: the EUV Connection Jorge
Sanz-Forcada and Andrea K. Dupree : p 256
Presentation 2
 Chemical Abundances in the Galactic Bulge Livia Origlia and R.
Michael Rich :p 347
 The Infrared View on Red Supergiant Stars Eric Josselin and
Bertrand Plez ; 405
 Stellar Populations in the Galactic Bulge Mathias Schultheis,
Bernhard Aringer, and Ariane Lan¸con : p 435
 The Prospects of Searching for Planets of Brown Dwarfs with
CRIRES Eike W. Guenther : p 487
 Probing Thick Planetary Atmospheres with High Resolution
Infrared Spectroscopy Catherine de Bergh and Bruno B´ezard ;
p513
 On the Variation of Cometary Polarisation Asoke K. Sen : p546