915 research outputs found
Explosions of LBV and Post-LBV Stars
In this contributed talk I presented the observational evidence for supernova (SN) explosions of stars in the luminous blue variable (LBV) and the immediate post-LBV evolutionary phases. We now have compelling indications that two recent SNe of Type II-ânarrowâ (IIn) were the explosions
of LBVs, including the direct identification of the progenitor LBV for one of these
examples. A recent SN of Type Ic exploded as a helium star, two years after
the powerful LBV outburst of its progenitor. These cases were also discussed
by other presenters at this Workshop in some detail. I instead focus more on
another example, SN2001em, which was first identified as a Type Ib/c, but later
evolved to Type IIn. I argue that the progenitor of this SN exploded as a Wolf-
Rayet (WR) star, following an eruptive LBV phase. Furthermore, I suggest that
two âSN impostors,â i.e., extragalactic massive stars observed to undergo pre-SN
LBV eruptions (similar to η Carinae), may well have evolved to the WR phase
in real time
Mid-Infrared Circumstellar Shell Sources Discovered with Spitzer: An Obscured Population of Massive Stars?
We have discovered a large number of circular and elliptical shells around luminous central sources at 24 ÎŒm with the MIPS instrument on board the Spitzer Space Telescope. Most of these shells are not visible in the shorter wavelengths bands of IRAC or archival 2MASS and optical images. On the other hand, many of the central stars are detected in the 2MASS catalog, but lack an optical counterpart, indicating that we are dealing with a population of highly obscured objects. Our archival follow-up effort has revealed 90% of these shell sources to be previously unknown
Molecular analysis of genetic diversity in a Texas maize (Zea mays L) breeding program
The Texas maize (Zea mays L) breeding program at Texas A&M University has been unique among breeding pro- grams for the incorporation of diverse germplasm from a wide range of origins into elite inbred lines. The Texas program, situated in a subtropical environment, has found beneficial traits in maize of tropical origin beyond what is available in the temperate material commonly used in the far more productive Midwestern region of the United States. To date, no molecular studies had been conducted to make any quantitative differentiations between the genetic diversity in the germplasm developed in the Texas program or comparisons to the germplasm available from the Midwest. In this study, a molecular characterization of genetic diversity was performed. A unique set of
266 elite Texas lines were genotyped using 766 single nucleotide polymorphism markers, this was then combined with data published in a previous study focusing on ex-PVP lines released by private companies. The two data sets combined had 380 genotypes with 635 markers. It was determined that there were five subpopulations of material in this combined set as demonstrated by population structure. The data suggested that the array mark- ers, designed to cluster the Midwestern heterotic groups, did not discriminate this exotic material well and/or that the Texas heterotic pools were not well supported. We conclude that the majority of Texas program material is a novel population, genetically dissimilar to Midwest temperate material, and would be a useful source of unique genetics for other maize breeding programs
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
Late-time Dust Emission from the Type IIn Supernova 1995N
Type IIn supernovae (SNe IIn) have been found to be associated with significant amounts of dust. These core-collapse events are generally expected to be the final stage in the evolution of highly massive stars, either while in an extreme red supergiant phase or during a luminous blue variable phase. Both evolutionary scenarios involve substantial pre-supernova mass loss. I have analyzed the SN IIn 1995N in MCG â02â38â017 (Arp 261), for which mid-infrared archival data obtained with the Spitzer Space Telescope in 2009 (~14.7 yr after explosion) and with the Wide-field Infrared Survey Explorer in 2010 (~15.6-16.0 yr after explosion) reveal a luminous (~2 Ă 10^7 L_â) source detected from 3.4 to 24 ÎŒm. These observations probe the circumstellar material, set up by pre-SN mass loss, around the progenitor star and indicate the presence of ~0.05-0.12 M_â of pre-existing, cool dust at ~240 K. This is at least a factor ~10 lower than the dust mass required to be produced from SNe at high redshift, but the case of SN 1995N lends further evidence that highly massive stars could themselves be important sources of dust
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
Searching for Progenitors of Core-Collapse Supernovae
Identifying the massive progenitor stars that give rise to core-collapse
supernovae is one of the main pursuits of supernova and stellar evolution
studies. In this talk I discuss some aspects of the pursuit of these progenitor
stars in ground-based and Hubble Space Telescope images.Comment: 6 pages, 4 figures, to appear in "1604-2004: Supernovae as
Cosmological Lighthouses," eds. M. Turatto, W. Shea, S. Benetti and L.
Zampieri, ASP Conference Serie
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