26 research outputs found
OB Stars in the Solar Neighborhood I: Analysis of their Spatial Distribution
We present a newly-developed, three-dimensional spatial classification
method, designed to analyze the spatial distribution of early type stars within
the 1 kpc sphere around the Sun. We propose a distribution model formed by two
intersecting disks -the Gould Belt (GB) and the Local Galactic Disk (LGD)-
defined by their fundamental geometric parameters. Then, using a sample of
about 550 stars of spectral types earlier than B6 and luminosity classes
between III and V, with precise photometric distances of less than 1 kpc, we
estimate for some spectral groups the parameters of our model, as well as
single membership probabilities of GB and LGD stars, thus drawing a picture of
the spatial distribution of young stars in the vicinity of the Sun.Comment: 28 pages including 9 Postscript figures, one of them in color.
Accepted for publication in The Astronomical Journal, 30 January 200
HI Shells Behind the Coalsack
We report the discovery of two new large HI shells in the direction of the
Coalsack nebula. Both shells were observed with the Parkes Radio Telescope as
part of the Southern Galactic Plane Survey. The largest shell, GSH 304-00-12,
is at a distance of ~1.2 kpc and has derived physical dimensions of 280 x 200
pc. The second shell, GSH 305+01-24, is at a distance of ~2.2 kpc and has
derived dimensions of 280 x 440 pc. We present a simple numerical model to show
that GSH 305+01-24 most likely formed from stellar winds in the Centaurus OB1
stellar association. There is associated radio, infrared and H-alpha continuum
emission. Both shells are situated in the Sagittarius-Carina arm, with GSH
305+01-24 more distant. The far edge of GSH 304-00-12 is at the near side of
the arm and opens into the interarm region. We find no evidence for closure at
the near side of the shell and therefore describe the geometry as conical.
Emission from the near side of the shell may be lost in absorption by the
Coalsack Nebula.Comment: 12 pages, 5 embedded EPS figures, uses emulateapj5.sty. To appear in
the Astrophysical Journal, vol. 56
X-ray and IR Point Source Identification and Characteristics in the Embedded, Massive Star-Forming Region RCW 108
We report on the results of an approximately 90 ks Chandra observation of a
complex region that hosts multiple sites of recent and active star formation in
ARA OB1a. The field is centered on the embedded cluster RCW 108-IR and includes
and a large portion of the open cluster NGC 6193. We detect over 420 X-ray
sources in the field and combined these data with deep near-IR, Spitzer/IRAC
and MSX mid-IR data. We find about 360 of the X-ray sources have near--IR
counterparts. We divide the region into 5 parts based on the X-ray point source
characteristics and extended 8 micron emission. The most clearly defined
regions are the central region - identified by embedded sources with high
luminosities in the both the near-IR and X-ray as well as high X-ray
temperatures (about 3 keV) and the eastern region - identified by low
extinction and 1 keV X-ray temperatures. Other regions, identified by their
directional relationship to RCW 108-IR are less uniform - representing
combinations of the first two regions, independent star formation epochs, or
both. Over 18% percent of the cluster members with over 100 counts exhibit
flares. Overall about 50% of the stars appear to have optically thick disks
when IRAC data are employed. The largest fraction of X-ray sources are best
described as possessing some disk material via a more detailed extinction
fitting. We estimate that the total number of pre--main sequence stars in the
field is about 1600. Approximately 800 are confined to (1.1 pc) central region.Comment: 63 pages including 18 figures, and 15 tables. Tables 1,2,5,7,10,and
11 have been stubbed in the text and included as ancillary files. Accepted by
the Astronomical Journa
The Effective Temperatures of Hot Stars II. The Early-O Types
We derive the stellar parameters of a sample of Galactic early-O type stars
by analysing their UV and Far-UV spectra from FUSE (905-1187A), IUE, HST-STIS
and ORFEUS (1200-2000A). The data have been modeled with spherical,
hydrodynamic, line-blanketed, non-LTE synthetic spectra computed with the
WM-basic code. We obtain effective temperatures ranging from Teff = 41,000 K to
39,000 K for the O3-O4 dwarf stars, and Teff = 37,500 K for the only supergiant
of the sample (O4 If+). Our values are lower than those from previous empirical
calibrations for early-O types by up to 20%. The derived luminosities of the
dwarf stars are also lower by 6 to 12%; however, the luminosity of the
supergiant is in agreement with previous calibrations within the error bars.
Our results extend the trend found for later-O types in a previous work by
Bianchi & Garcia.Comment: Accepted for publication in The Astrophysical Journal. 38 pages
(including 9 figures and 4 tables
Strømgren and H
Strømgren and Hβ
photometry of 130 stars in the Carina section of the Milky Way is presented.
The color excesses and the distances of all stars are obtained. A good
agreement is found between the CM and HR diagrams and the spatial
distribution of these stars