J/A+AS/109/313 Heterochromatic Atmospheric Extinction (Roberts+, 1995)
Heterochromatic extinction. II. Dependence of interstellar extinction
on stellar temperature, surface gravity, and metallicity.
Roberts W.J., Grebel E.K.
<Astron. Astrophys. Suppl. Ser. 109, 313 (1995)>
=1995A&AS..109..313R 1995A&AS..109..313R
ADC_Keywords: Extinction; Stars, atmospheres
Keywords: atmospheric effects - techniques: photometric -
stars: fundamental parameters
Abstract:
In synthetic versions of two broadband photometric systems,
Johnson-Cousins and Washington, we find the dependence of atmospheric
extinction corrections on colour and on macro features in the spectra
of stars, such as the Balmer jump, as parameterised by Teff, logg, and
[Fe/H]. We use standard passbands, a mean atmospheric extinction law
measured at ESO/La Silla, extended and modified by us, and the Kurucz
library of synthetic spectra.
The true broadband atmospheric extinction is far more complicated than
any current reduction (transformation) methods consider. Hence all
broadband magnitude systems are fundamentally unphysical - they
contain not the extra-atmospheric magnitudes, but unobservable
magnitudes whose relation to physical magnitudes is unknown, but may
differ by 0.05mag or more for hot and cool stars. Hence, it is
hazardous to compare them to any synthetic magnitude system derived
from either synthetic spectra or spectral scans. These problems exist
to a lesser degree in intermediate band systems, but narrow band
systems are relatively immune from these complexities.
We do not treat either kind of system here. If our results were
incorporated into a photometric reduction program, and standard stars
and program stars stars carefully selected by metallicity and
luminosity class, a standard magnitude system could be established
that would be directly comparable to synthetic systems. As a bonus,
measurements of intrinsic flux variations at the millimagnitude level
would become more secure. We describe our own operational photometric
transformation program that incorporates only the linear part of the
dependence on colour of atmospheric extinction. Our results and
prescriptions are useful for aperture photoelectric photometry, but
our implementation is aimed at CCD photometry of stellar populations.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
coeff1.dat 64 144 *Rational polynomial coefficients
coeff2.dat 189 144 *Actual coefficients
diffb.dat 139 638 Differential atmospheric extinction in UBVRI
diffw.dat 139 638 Differential atmospheric extinction in CMT1T2
totb.dat 75 638 Total atmospheric extinction in UBVRI
totw.dat 65 638 Total atmospheric extinction in CMT1T2
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Note on coeff1.dat, coeff2.dat: These tables show the coefficients of fits
purely linear in temperature colour to the interstellar extinctions
for all passbands considered. The lowest temperature model, 3500K, was
excluded from ALL fits to B-V, because it is badly behaved there. The
same temperature was also excluded from the fits to V-I and M-T2 for
[Fe/H]=-2.0, because these temperature colours are not monotonic there.
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Byte-by-byte Description of file: totb.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Star Star type (G1)
4- 7 F4.1 [Sun] [Fe/H] Metallicity
10- 15 F6.0 K Teff Effective temperature
19- 25 F7.5 mag K(U)X Total atmospheric extinction coefficient in U
for airmass 1 (because U filter is defined by
atmospheric cutoff, see paper II)
29- 35 F7.5 mag K(B)X Total atmospheric extinction coefficient in B
for airmass 1 (to allow calculation of U-B.)
39- 45 F7.5 mag K(B) Total atmospheric extinction coefficient in B
for airmass 0
49- 55 F7.5 mag K(V) Total atmospheric extinction coefficient in V
for airmass 0
59- 65 F7.5 mag K(R) Total atmospheric extinction coefficient in R
for airmass 0
69- 75 F7.5 mag K(I) Total atmospheric extinction coefficient in I
for airmass 0
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Byte-by-byte Description of file: diffb.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Star Star type (G1)
4- 7 F4.1 [Sun] [Fe/H] Metallicity
9- 14 F6.0 K Teff effective temperature
17- 23 F7.4 mag U-B (U-B) colour index
26- 31 F6.4 --- K(U-B) Differential atmospheric extinction
coefficient in (U-B)
34- 39 F6.4 --- R1 K(U-B)/K(B-V) ratio
42- 48 F7.4 mag B-V (B-V) colour index
51- 56 F6.4 --- K(B-V) Differential atmospheric extinction
coefficient in (B-V)
59- 64 F6.4 --- R2 K(B-V)/K(B-V) ratio
67- 73 F7.4 mag V-R (V-R) colour index
76- 81 F6.4 --- K(V-R) Differential atmospheric extinction
coefficient in (V-R)
84- 89 F6.4 --- R3 K(V-R)/K(B-V) ratio
92- 98 F7.4 mag R-I (R-I) colour index
101-106 F6.4 --- K(R-I) Differential atmospheric extinction
coefficient in (R-I)
109-114 F6.4 --- R4 K(R-I)/K(B-V) ratio
117-123 F7.4 mag V-I (V-I) colour index
126-131 F6.4 --- K(V-I) Differential atmospheric extinction
coefficient in (V-I)
134-139 F6.4 --- R5 K(V-I)/K(B-V) ratio
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Byte-by-byte Description of file: totw.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Star Star type (G1)
4- 7 F4.1 [Sun] [Fe/H] Metallicity
10- 15 F6.0 K Teff Effective temperature
19- 25 F7.5 --- KC Total atm. ext. for C Washington band
29- 35 F7.5 --- KM Total atm. ext. for M Washington band
39- 45 F7.5 --- KT1 Total atm. ext. for T1 Washington band
49- 55 F7.5 --- KT2 Total atm. ext. for T2 Washington band
59- 65 F7.5 --- K51 Total atm. ext. for DDO 51 Washington band
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Byte-by-byte Description of file: diffw.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Star Star type (G1)
4- 7 F4.1 [Sun] [Fe/H] Metallicity
9- 14 F6.0 K Teff effective temperature
17- 23 F7.4 mag C-M (C-M) colour index
26- 31 F6.4 --- K(C-M) Differential atmospheric extinction
coefficient for (C-M)
34- 39 F6.4 --- R1 K(C-M)/K(M-T2) ratio
42- 48 F7.4 mag M-T1 (M-T1) colour index
51- 56 F6.4 --- K(M-T1) Differential atmospheric extinction
coefficient for (M-T1)
59- 64 F6.4 --- R2 K(M-T1)/K(M-T2) ratio
67- 73 F7.4 mag T1-T2 (T1-T2) colour index
76- 81 F6.4 --- K(T1-T2) Differential atmospheric extinction
coefficient for (T1-T2)
84- 89 F6.4 --- R3 K(T1-T2)/K(M-T2) ratio
92- 98 F7.4 mag M-T2 (M-T2) colour index
101-106 F6.4 --- K(M-T2) Differential atmospheric extinction
coefficient for (M-T2)
109-114 F6.4 --- R4 K(M-T2)/K(M-T2) ratio
117-123 F7.4 mag M-51 (M-DDO51) colour index
125-131 F7.4 --- K(M-51) Differential atmospheric extinction
coefficient for (M-DDO51)
133-139 F7.4 --- R5 K(M-51)/K(M-T2) ratio
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Byte-by-byte Description of file: coeff1.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Filter Filters or quantity involved (1)
4- 8 A5 --- Band Quantity, e.g., filter or colour
12- 14 F3.1 [cm/s2] logg []? Surface gravity
15 A1 --- n_logg [m ] Lowest surface gravity model when there
is no value for logg (2)
19- 22 F4.1 [Sun] [Fe/H] Metallicity
27 I1 --- num Numerator degree (3)
33 I1 --- den Denominator degree (3)
40- 49 E10.4 --- MaxDev Largest deviation (4)
52- 57 F6.3 --- TCmin Lower boundary of the valid range of
temperature colour for that fit (5)
60- 64 F5.3 --- TCmax Upper boundary of the valid range of
temperature colour for that fit (5)
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Note (1): the conventions are:
UB = U, U-B
BR = B, B-R
BV = V, B-V
VI = V-I
CM = C, C-M
M1 = M, M-T1
M2 = M-T2
Note (2): 'm' means the lowest surface gravity model for that temperature
in the Kurucz models, i.e., the SG=supergiants
Note (3): Degree of the numerator and the denominator of the best fitting
rational polynomial found (in some cases a linear fit was chosen
without searching for a higher order fit). The numerator always stars
with a_0, so there is one more coefficient in the numerator than the
degree. The denominator starts with b1.
Note (4): Largest deviation in extinction of the rational polynomial
from any of the data points in the interstellar extinction table (dif*
and tot*) for that fit, as returned by the Numerical Recipes routine
'ratlsq'.
Note (5): For the atmospheric extinctions the TCs are V-I and M-T2.
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Byte-by-byte Description of file: coeff2.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Band Quantity, e.g., filter or colour
10- 12 F3.1 [cm/s2] logg []? Surface gravity
13 A1 --- n_logg [m ] Lowest surface gravity model when there
is no value for logg (1)
17- 20 F4.1 [Sun] [Fe/H] Metallicity
22- 32 E11.4 --- a0 Coefficient a0 in the numerator
34- 44 E11.4 --- a1 Coefficient a1 in the numerator
46- 56 E11.4 --- a2 []? Coefficient a2 in the numerator
58- 68 E11.4 --- a3 []? Coefficient a3 in the numerator
70- 80 E11.4 --- a4 []? Coefficient a4 in the numerator
82- 92 E11.4 --- a5 []? Coefficient a5 in the numerator
94-104 E11.4 --- a6 []? Coefficient a6 in the numerator
106-116 E11.4 --- a7 []? Coefficient a7 in the numerator
119-129 E11.4 --- b1 []? Coefficient b1 in the denominator
131-141 E11.4 --- b2 []? Coefficient b2 in the denominator
143-153 E11.4 --- b3 []? Coefficient b3 in the denominator
155-165 E11.4 --- b4 []? Coefficient b4 in the denominator
167-177 E11.4 --- b5 []? Coefficient b5 in the denominator
179-189 E11.4 --- b6 []? Coefficient b6 in the denominator
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Note (1): 'm' means the lowest surface gravity model for that
temperature in the Kurucz models, i.e., the SG=supergiants
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Global Notes:
Note (G1): the types are:
MS = Main Sequence,
RG = Red Giants (log(g)=2.5),
SG = SuperGiants (i.e., the lowest surface gravity for that
temperature in the Kurucz model family).
(End) Patricia Bauer [CDS] 07-Sep-1994