1,022 research outputs found
Red Eyes on Wolf-Rayet Stars: 60 New Discoveries via Infrared Color Selection
We have spectroscopically identified 60 Galactic Wolf-Rayet (WR) stars,
including 38 nitrogen types (WN) and 22 carbon types (WC). Using photometry
from the Spitzer/GLIMPSE and 2MASS databases, the WRs were selected via a
method we have established that exploits their unique infrared colors, which is
mainly the result of excess radiation from free-free scattering within their
dense ionized winds. The selection criteria has been refined since our last
report, and now yields WRs at a rate of ~20% in spectroscopic follow-up of
candidates that comprise a broad color space defined by the color distribution
of all known WRs having B>14 mag. However, there are subregions within the
broad color space which yield WRs at a rate of >50%. Cross-correlation of WR
candidates with archival X-ray point-source catalogs increases the WR detection
rate of the broad color space to ~40%; ten new WR X-ray sources have been
found, in addition to a previously unrecognized X-ray counterpart to a known
WR. The extinction values, distances, and galactocentric radii of all new WRs
are calculated using the method of spectroscopic parallax. Although the
majority of the new WRs have no obvious association with stellar clusters, two
WC8 stars reside in a previously unknown massive-star cluster that lies near
the intersection of the Scutum-Centaurus Arm and the Galaxy's bar, in which
five OB supergiants were also identified. In addition, two WC and four WN stars
were identified in association with the stellar clusters Danks 1 and 2. A WN9
star has also been associated with the cluster [DBS2003] 179. This work brings
the total number of known Galactic WRs to 476, or ~7-8% of the total
empirically estimated population. An examination of their Galactic distribution
reveals a tracing of spiral arms and an enhanced WR surface density toward
several massive-star formation sites (abridged).Comment: Accepted to the Astronomical Journal on May 20, 2011. Document is 39
pages, including 20 figures and 8 table
12 New Galactic Wolf-Rayet Stars Identified via 2MASS+Spitzer/GLIMPSE
We report new results from our effort to identify obscured Wolf-Rayet stars
in the Galaxy. Candidates were selected by their near-infrared (2MASS) and
mid-infrared (Spitzer/GLIMPSE) color excesses, which are consistent with
free-free emission from ionized stellar winds and thermal excess from hot dust.
We have confirmed 12 new Wolf-Rayet stars in the Galactic disk, including 9 of
the nitrogen subtype (WN), and 3 of the carbon subtype (WC); this raises the
total number of Wolf-Rayet stars discovered with our approach to 27. We
classify one of the new stars as a possible dust-producing WC9d+OBI
colliding-wind binary, as evidenced by an infrared excess resembling that of
known WC9d stars, the detection of OBI features superimposed on the WC9
spectrum, and hard X-ray emission detected by XMM-Newton. A WC8 star in our
sample appears to be a member of the stellar cluster Danks 1, in contrast to
the rest of the confirmed Wolf-Rayet stars that generally do not appear to
reside within dense stellar clusters. Either the majority of the stars are
runaways from clusters, or they formed in relative isolation. We briefly
discuss prospects for the expansion and improvement of the search for
Wolf-Rayet stars throughout the Milky Way Galaxy.Comment: Submitted to PASP March 12, 2009; Accepted on May 14, 200
A unified supernova catalogue
In this paper a new supernova catalogue containing data for 5526
extragalactic supernovae that were discovered up to 2010 December 31 is
presented. It combines several catalogues that are currently available online
in a consistent and traceable way. During the comparison of the catalogues
inconsistent entries were identified and resolved where possible. Remaining
inconsistencies are marked transparently and can be easily identified. Thus it
is possible to select a high-quality sample in a most simple way. Where
available, redshift-based distance estimates to the supernovae were replaced by
journal-refereed distances. Examples of statistical studies that are now
possible with this new catalogue are presented in this paper.Comment: 9 pages, 12 figures, catalogue is available at
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/538/A12
Applications of Machine-Learning Algorithms for Infrared Colour Selection of Galactic Wolf-Rayet Stars
We have investigated and applied machine-learning algorithms for Infrared
Colour Selection of Galactic Wolf-Rayet (WR) candidates. Objects taken from the
GLIMPSE catalogue of the infrared objects in the Galactic plane can be
classified into different stellar populations based on the colours inferred
from their broadband photometric magnitudes (, and from 2MASS, and
the four \textit{Spitzer}/IRAC bands). The algorithms tested in this pilot
study are variants of the -Nearest Neighbours (-NN) approach, which is
ideal for exploratory studies of classification problems where interrelations
between variables and classes are complicated. The aims of this study are (1)
to provide an automated tool to select reliable WR candidates and potentially
other classes of objects, (2) to measure the efficiency of infrared colour
selection at performing these tasks and, (3) to lay the groundwork for
statistically inferring the total number of WR stars in our Galaxy. We report
the performance results obtained over a set of known objects and selected
candidates for which we have carried out follow-up spectroscopic observations,
and confirm the discovery of 4 new WR stars.Comment: Authors' version of published paper, now at MNRAS, 473, 256
A Massive Progenitor of the Luminous Type IIn Supernova 2010jl
The bright, nearby, recently discovered supernova SN2010jl is a member of the
rare class of relatively luminous Type~IIn events. Here we report archival HST
observations of its host galaxy UGC5189A taken roughly 10yr prior to explosion,
as well as early-time optical spectra of the SN. The HST images reveal a
bright, blue point source at the position of the SN, with an absolute magnitude
of -12.0 in the F300W filter. If it is not just a chance alignment, the source
at the SN position could be (1) a massive young (less than 6 Myr) star cluster
in which the SN resided, (2) a quiescent, luminous blue star with an apparent
temperature around 14,000K, (3) a star caught during a bright outburst akin to
those of LBVs, or (4) a combination of option 1 and options 2 or 3. Although we
cannot confidently choose between these possibilities with the present data,
any of them imply that the progenitor of SN2010jl had an initial mass above
30Msun. This reinforces mounting evidence that many SNe IIn result from very
massive stars, that massive stars can produce visible SNe without collapsing
quietly to black holes, and that massive stars can retain their H envelopes
until shortly before explosion. Standard stellar evolution models fail to
account for these observed properties.Comment: 6 pages, 4 figures, submitted to Ap
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