J/A+A/536/A101 UBVI photometry towards (l=314,b=0) (Carraro, 2011)
Photometric distances to young stars in the inner Galactic disk.
I. The L = 314° direction.
Carraro G.
<Astron. Astrophys. 536, A101 (2011)>
=2011A&A...536A.101C 2011A&A...536A.101C
ADC_Keywords: Milky Way ; Photometry, CCD ; Photometry, UBVRI
Keywords: open clusters and association: general - stars: early type -
Galaxy: disk
Abstract:
The spiral structure of the Milky Way is nowadays receiving renewed
attention thanks to the combined efforts of observational campaigns in
different wavelength regimes, from the optical to the radio.
We start in the paper the exploration of a number of key sectors (line
of sights) in the inner Milky Way, where the spiral structure is still
poorly known.
We search for density enhancements of young stars that might plausibly
be associated with spiral structure. To this aim we collect
sufficiently wide-field UBVI photometry to allow us to probe in
statistical sense the distribution in reddening and distance of young
stars in the field. The intensive usage of U-band photometry -
although heavily demanding in terms of observational efforts - ensures
robust determination of reddening and hence distance for stars of
spectral type earlier than A0, which are well-known spiral arm
tracers, even though no spectroscopic information are available.
The fields we use are large enough to include in most cases
well-studied Galactic clusters, which we use as bench-marks to assess
the quality and standardisation of the data, and to validate our
method.
We focus in this paper on the line of sight to the Galactic longitude
l=314°, where previous surveys already detected Hα emitters
at different standard of rest velocities, and hence distances. The
difficulty, however, to translate velocity into distance make
predictions on the spiral structure quite vague.
First of all, we made exhaustive tests to show that our data-set is in
the standard system, and calibrated our method using the two open
clusters NGC 5617 and Pismis 19 which happen to be in the field, and
for which we found estimates of the basic parameters in full agreement
with the literature.
We then applied the method to the general field stars and detected
signatures of three different groups of stars, evenly distributed
across the field of view, at 1.5+0.5-0.2, 2.5+0.3-0.5,
and 5.1+1.5-1.1kpc, respectively. These distances are
compatible with the location of the nowadays commonly accepted
description of the Carina-Sagittarius and Scutum-Crux arms, at
heliocentric distance of ∼2 an 5kpc, respectively. As a consequence,
we consider these groups to be good candidates to trace the location
of these two inner arms.
In line with previous studies, this investigation demonstrates once
again how powerful the use of U-band photometry is to characterize
ensembles of young stars, and make predictions on the spiral structure
of the Milky Way.
Description:
UBVI CCD photometry in a Galactic field centered at RA=14:30:00.8,
DE=-60:48:25.7. The field is 14.8x22.8arcmin2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 87 3003 Star positions and photometry
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq Sequential number of the star
7- 17 F11.7 deg RAdeg Right ascension (J2000.0)
19- 29 F11.7 deg DEdeg Declination (J2000.0)
31- 37 F7.4 mag Vmag Johnson V magnitude
39- 44 F6.4 mag e_Vmag Error in V magnitude
46- 52 F7.4 mag U-B Johnson U-B color index
54- 59 F6.4 mag e_U-B Error in U-B color index
61- 66 F6.4 mag B-V Johnson B-V color index
68- 73 F6.4 mag e_B-V Error in B-V color index
75- 80 F6.4 mag V-Ic Johnson-Cousins V-I color index
82- 87 F6.4 mag e_V-Ic Error in V-Ic color index
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Acknowledgements:
Giovanni Carraro, gcarraro(at)eso.org
(End) Giovanni Carraro [ESO, Chile], Patricia Vannier [CDS] 27-Oct-2011