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Title: Distribution of interstellar matter in the galactic disk from visual
extinction data
I. The catalogue of extinctions and distances
Author: J. Guarinos
Abstract: As a preliminary step towards a new study of the interstellar medium
in the solar vicinity from visual interstellar extinction data, we built a large
catalogue of stars with estimated visual extinction A_V_ and distance, using
reliable UBV data and MK types. Before this, we discarded the stars with wrong
spectral classifications, the binary stars, the metal deficient stars, the
variable stars and the chemically peculiar ones. While building the catalogue, a
special attention was paid to the consistency between the spectroscopic and
photometric data. The program designed for computing extinctions and distances
is described in details in the corresponding paper (Astron. Astrophys. Suppl.
Ser., submitted). For each star, this program performs a choice of the "best" MK
type and the assignment of an absolute magnitude and of an intrinsic colour. All
the observed data and derived parameters of the selected stars as well as of
some of the discarded ones were put in computer-readable files which are
distributed by the Centre de Donnees astronomiques de Strasbourg (CDS). From
more than 160000 objects with an MK type and about 90000 ones with UBV data,
only 16300 stars remain in the final list, among which, 15449 stars have
distances not larger than 3000 pc. These are the stars of the two files of our
catalogue. The latter is much more homogeneous in spectral types than the
catalogues previously used for drawing maps of the interstellar matter,
especially regarding the repartition between O/B and A/F stars, allowing a more
uniform spatial distribution of the sample of stars in the galactic disc near
the Sun.
Keywords: stars: distances -- stars: fundamental parameters -- dust, extinction
-- solar neighbourhood -- catalogs
Section: Construction of a catalogue of interstellar extinctions and stellar
distances
subSection: Data sources The V magnitudes and the (B-V) and (U-B) colour indices
were given by the compilation of Mermilliod (1987). It contains 136700 entries,
concerning 87300 stars. Each star may have several measurements of the V
magnitude or of one or both of the colour indices.
The MK types were provided by several catalogues. The most important in volume
is the University of Michigan Catalogue of Two-Dimensional Spectral Types for
the HD Stars (Houk & Cowley 1975; Houk 1978; Houk 1982; Houk & Smith-Moore
1988). It contains the MK types of 130400 southern stars. All the visual
spectral classifications were performed by Houk, which makes this catalogue the
most homogeneous available now. We discarded the spectral classifications
inferred from under-exposed and superposed spectra: only the MK types inferred
from quality 1 and 2 spectra were selected for the construction of our catalogue
(Houk assigns four qualities to her spectra).
The second most important source of our MK types was the Catalogue of Selected
Spectral Types in the MK System (M. Jaschek 1978), which contains a selected MK
type for about 30400 stars in the two hemispheres. M. Jaschek's and Houk's
spectral classifications catalogues, whose intersection is not empty, are the
largest such catalogues available now. In addition, they are very close to the
original system of Morgan and Keenan. This is why, in spite of the better
resolution achievable nowadays, we took the spectral types and luminosity
classes from these two sources for the majority of our catalogue stars: We
preferred homogeneity rather than precision. The Third General Catalogue of MK
Spectral Classification (Buscombe 1977) and the Jensen's catalogue (1983) were
also used when no reliable MK type was available in the two main sources.
Section: The final catalogues After the selection process, we got 16307 selected
stars of all spectral types, all luminosity classes and all distances, gathered
in a computer-readable file called "DistEx" (for Distances and Extinctions)
available from the author on request. Among these stars, there are members of
other galaxies (the small and large magellanic clouds) as well as stars
belonging to globular clusters and whose metal-deficiency escaped from the
selection process. In order to keep only the members of our galaxy having
reliable enough distances, we selected the stars which have been given a
distance of less than 3000 pc. They are 15449 in number. This set of data, the
Catalogue of Extinctions and Distances Derived from UBV data (CEDDU) is the main
output of the work presented in this paper. It has been stored in two
computer-readable files. So were the sets of data concerning some stars which
were discarded during the selection process. The latter need new observations
and are interesting candidates for further spectroscopic studies in the optical
and in the UV, with higher resolution.
All these catalogs and related technical informations can be obtained from the
Centre de Donnees astronomiques de Strasbourg (CDS), 11 rue de l'Universite,
F--67000 Strasbourg, France.
subSection: Content of the Catalogue of Extinctions and Distances Derived from
UBV data (CEDDU) CEDDU contains 15449 stars of all spectral types, all
luminosity classes and with distances not larger than 3000 pc. The informations
on them are stored in two files, having both a record length of 132 bytes. The
first one, CEDDU1, displays a selection of observational data along with all the
derived and computed parameters, such as absolute magnitude, intrinsic colour
(B-V)_o_, interstellar extinction A_V_ and heliocentric distance. The second
file, CEDDU2, contains the complete set of observational data. Both files are
sorted in ascending galactic longitudes.
For each star, CEDDU1 displays the following data:
(o) Bytes 1-12: The identifier (either a HD number or a DM number).
(o) Bytes 14-35: The MK type written in a standard format.
(o) Byte 36: A letter indicating the source of the MK type:
(o) "H" indicates that the MK type comes from the Michigan Spectral Catalogue
(Houk & Cowley 1975; Houk 1978; Houk 1982; Houk & Smith-Moore 1988).
(o) "J" indicates that the MK type comes from the Catalogue of Selected Spectral
Types in the MK System (M. Jaschek 1978).
(o) "B" indicates that the MK type was found in the Third General Catalogue of
MK Spectral Classification (Buscombe 1977).
(o) "K" indicates that the MK type was found in the catalogue of Jensen (1983).
(o) Finally, for a very small number of stars, the MK type was found in the list
of spectral classifications provided by SIMBAD. These MK types are indicated by
"S".
(o) Bytes 39-44: The apparent magnitude V in the UBV system. This value is the
average of all the non-deviating measurements provided by the Photoelectric
Photometric Catalogue (Mermilliod 1987).
(o) Bytes 46-51: The (B-V) colour index in the UBV system. This value is the
average of all the non-deviating measurements provided by the Photoelectric
Photometric Catalogue (Mermilliod 1987).
(o) Bytes 53-58: The (U-B) colour index in the UBV system. This value is the
average of all the non-deviating measurements provided by the Photoelectric
Photometric Catalogue (Mermilliod 1987).
(o) Bytes 62-66: The absolute magnitude of the star. The absolute magnitude
determination is described in section 3.3.2. of the paper.
(o) Bytes 68-71: A string of 4 characters indicating the source of the table
which provided the absolute magnitudes (see section 3.3.2):
(o) "GRMK" indicates that the absolute magnitude comes from the Grenier et al.
(1985) MK/M_V_ correspondence table for magnitude-limited samples.
(o) "CGMK" indicates that the absolute magnitude comes from the Corbally and
Garrison (1984) MK/M_V_ correspondence table.
(o) "SKMK" indicates that the absolute magnitude comes from the Schmidt-Kaler
(1982) MK/M_V_ correspondence table.
(o) "SKMQ" indicates that the absolute magnitude comes from the Schmidt-Kaler
(1982) (B-V)_o_-Luminosity class/M_V_ correspondence table. In this case, the
intrinsic colour (B-V)_o_ necessary for the use of this table has been computed
through a photometric method exposed in section 3.3.1. (see Garcia, Claria and
Levato 1988).
(o) Bytes 75-79: The intrinsic colour (B-V)_o_.
(o) Bytes 81-84: A string of either 2 or 4 characters indicating how the
intrinsic colour was determined (see section 3.3.1):
(o) "MQ" indicates that the photometric method described in section 3.3.1 was
used to compute (B-V)_o_. This method, an update of the one proposed by Johnson
& Morgan (1953), is explained by Garcia et al. (1988).
(o) "SK" indicates that the intrinsic colour comes from the MK/(B-V)_o_
correspondence table (Schmidt-Kaler 1982).
(o) "SK--n", where n is an integer whose value is either 1 or 2, indicates that
a correction of n sub-types towards the blue has been performed on the spectral
type, before using the MK/(B-V)_o_ correspondence table (Schmidt-Kaler 1982).
(o) For 10 stars, a correction of 1 sub-type towards the blue has been performed
on the spectral type, before using the updated Q method described by Garcia et
al. (1988). "MQ--1" corresponds to these stars.
(o) Bytes 87-91: The interstellar extinction A_V_, in magnitudes. It has been
calculated as explained in section 3.3.1.
(o) Bytes 94-97: The heliocentric distance d, in parsecs.
(o) Bytes 100-103: The X-coordinate in the galactic plane, in parsecs: X = d cos
b sin l, where l and b are the galactic latitude and longitude.
(o) Bytes 105-109: The Y-coordinate in the galactic plane, in parsecs: Y = -d
cos b cos l, where l and b are the galactic latitude and longitude.
(o) Bytes 111-115: The Z-coordinate or height above the galactic plane, in
parsecs: Z = d sin b, where b is the galactic latitude.
(o) Bytes 119-124: The galactic longitude l.
(o) Bytes 126-131: The galactic latitude b.
CEDDU2 provides a more complete information on photometric and spectroscopic
observational data, along with the equatorial coordinates (for equinox 2000).
Its content is the following:
(o) Bytes 1-12: The identifier (either a HD number or a DM number).
(o) Bytes 14-45: The MK type written in a same standard format as in CEDDU1,
with all the spectrum peculiarities (if there are). Their source is identical to
that of the MK type.
(o) Byte 46: A letter indicating the source of the MK type, as in CEDDU1.
(o) Bytes 49-56: The right ascension (equinox 2000).
(o) Bytes 59-66: The declination (equinox 2000).
(o) Bytes 69-74: The galactic longitude.
(o) Bytes 76-81: The galactic latitude.
(o) Bytes 83-88: The apparent magnitude V in the UBV system. This value is the
average of all the non-deviating measurements provided by the Photoelectric
Photometric Catalogue (Mermilliod 1987).
(o) Bytes 89-91: The number of measurements with which the apparent magnitude V
was calculated.
(o) Bytes 93-98: The rms of the apparent magnitude V.
(o) Bytes 100-105: The (B-V) colour index in the UBV system. This value is the
average of all the non-deviating measurements provided by the Photoelectric
Photometric Catalogue (Mermilliod 1987).
(o) Bytes 106-108: The number of measurements with which the (B-V) colour index
was calculated.
(o) Bytes 110-115: The rms of the (B-V) colour index.
(o) Bytes 117-122: The (U-B) colour index in the UBV system, if available. This
value is the average of all the non-deviating measurements provided by the
Photoelectric Photometric Catalogue (Mermilliod 1987).
(o) Bytes 123-125: The number of measurements with which the (U-B) colour index
was calculated.
(o) Bytes 127-132: The rms of the (U-B) colour index. Among the 15449 stars of
CEDDU, 11911 are closer than 120 pc from the galactic plane (-120 pc <= Z <= 120
pc). Note that the proportion of stars for which the (U-B) colour index is
available is approximately 82 %.
subSection: Contents of the appendices
subsubSection: Stars with negative colour excesses Our selection process
isolated 390 stars for which the estimated E_B-V_ is negative, even after a two
spectral sub-types shift towards the blue. These stars were put in dedicated
computer-readable files. The data equivalent to those of CEDDU1 are stored in
the file exneg1, except that:
(o) The absolute magnitude has not been calculated and is, therefore, missing,
as well as its source.
(o) The interstellar extinction A_V_ is replaced by the colour excess E_B-V_ and
shifted by one byte towards the right.
(o) The distance d, X, Y and Z have not been calculated.
(o) The galactic longitude and latitude are missing. The file exneg2 has the
same type of content as CEDDU2, with the same organisation.
subsubSection: Apparent very close stars with heavy reddening Our program
discarded 62 stars because it computes an extinction above 0.5 with a distance
below 20 pc for them. These stars were put in dedicated computer-readable files.
The data equivalent to those of CEDDU1 are stored in the file avlar1, except
that:
(o) The distance d, X, Y and Z are shifted towards the right: They are written
between bytes 96 and 120.
(o) The galactic longitude and latitude are missing. The file avlar2 has the
same type of content as CEDDU2, with the same organisation.
subsubSection: Apparent very far stars with low reddening Our program discarded
98 stars because it computes an extinction of less than 0.2 mag/kpc along the
portion of sightline which goes across the galactic disk (with an assumed
thickness of 120 pc) and a distance of more than 1 kpc. It is possible that
these stars really exhibit a very low extinction. They were removed from the
catalogue only because their extinction is considered as statistically abnormal.
The data equivalent to those of CEDDU1 are stored in the file asmal1, except
that:
(o) The distance d, X, Y and Z are shifted towards the right: They are written
between bytes 96 and 120.
(o) The galactic longitude and latitude are missing. The file asmal2 has the
same type of content as CEDDU2, with the same organisation.
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Corbally, C. J., Garrison, R. F. : 1984, in The MK Process and Stellar
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Garrison Ed. p. 277.
Garcia, B., Claria, J. J., Levato, H. : 1988, Astrophys. Sp. Sci. 143, 317.
Grenier, S., Gomez, A. E., Jaschek, C., Jaschek, M., Heck, A. : 1985, Astron.
Astrophys. 145, 331.
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