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J/A+AS/109/313 Heterochromatic extinction. II. (Roberts+, 1995)
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Heterochromatic extinction. I. 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 (SIMBAD/NED Reference)
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ADC_Keywords: Extinction; Interstellar medium; 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 T_eff_, 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 64 144 *Rational polynomial coefficients
coeff2 189 144 *Actual coefficients
diffb 139 638 Differential atmospheric extinction in UBVRI
diffw 139 638 Differential atmospheric extinction in CMT1T2
totb 75 638 Total atmospheric extinction in UBVRI
totw 65 638 Total atmospheric extinction in CMT1T2
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Note on coeff1 & coeff2: 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.
Byte-by-byte Description of file: totb
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Bytes Format Units Label Explanations
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1- 2 A2 --- Star Star type (1)
4- 7 F4.1 mag [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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Note (1): 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).
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Byte-by-byte Description of file: diffb
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Bytes Format Units Label Explanations
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1- 2 A2 --- Star Star type (1)
4- 7 F4.1 mag [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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Note (1): 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).
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Byte-by-byte Description of file: totw
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Bytes Format Units Label Explanations
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1- 2 A2 --- Star Star type (1)
4- 7 F4.1 mag [Fe/H] Metallicity
10- 15 F6.0 K Teff Effective temperature
19- 25 F7.5 --- KC Total atm. ext. for C
29- 35 F7.5 --- KM Total atm. ext. for M
39- 45 F7.5 --- KT1 Total atm. ext. for T1
49- 55 F7.5 --- KT2 Total atm. ext. for T2
59- 65 F7.5 --- K51 Total atm. ext. for DDO 51
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Note (1): 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).
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Byte-by-byte Description of file: diffw
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Bytes Format Units Label Explanations
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1- 2 A2 --- Star Star type (1)
4- 7 F4.1 mag [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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Note (1): 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).
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Byte-by-byte Description of file: coeff1
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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 mag [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): 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 b_1.
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
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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 mag [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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(End) Patricia Bauer [CDS] 07-Sep-1994