32 research outputs found
Analysis of B and Be Star Populations of the Double Cluster h and chi Persei
We present blue optical spectra of 92 members of h and chi Per obtained with
the WIYN telescope at Kitt Peak National Observatory. From these spectra,
several stellar parameters were measured for the B-type stars, including V sin
i, T_eff, log g_polar, M_star, and R_star. Stromgren photometry was used to
measure T_eff and log g_polar for the Be stars. We also analyze photometric
data of cluster members and discuss the near-to-mid IR excesses of Be stars.Comment: 4 pages, to appear in the proceedings of IAU Symposium 266: Star
Cluster
The Distance of the Gamma-ray Binary 1FGL J1018.6-5856
The recently discovered gamma-ray binary 1FGL J1018.6-5856 has a proposed
optical/near-infrared (OIR) counterpart 2MASS 10185560-5856459. We present
Stromgren photometry of this star to investigate its photometric variability
and measure the reddening and distance to the system. We find that the
gamma-ray binary has E(B-V) = 1.34 +/- 0.04 and d = 5.4^+4.6_-2.1 kpc. While
E(B-V) is consistent with X-ray observations of the neutral hydrogen column
density, the distance is somewhat closer than some previous authors have
suggested.Comment: Accepted to PAS
Spectroscopic Hα and Hγ survey of field Be stars: 2004-2009
Massive O- and B-type stars are cosmic engines in the Universe and can be the dominant source of luminosity in a galaxy. The class of Be stars are rapidly rotating B-type stars that lose mass in an equatorial, circumstellar disk (Porter & Rivinius 2003) and cause Balmer and other line emission. Currently, we are unsure as to why these stars rotate so quickly but three scenarios are possible: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence evolution of B stars. In order to investigate these scenarios for this population of massive stars, we have been spectroscopically observing a set of 115 field Be stars with the Kitt Peak Coudè Feed telescope in both the Hα and Hγ wavelength regimes since 2004. This time baseline allows for examination of variability properties of the circumstellar disks as well as determine candidates for closer examination for binarity. We find that 90% of the observed stars show some variability with 8% showing significant variability over the 5-year baseline. Such values may be compared with the significant variability seen in some clusters such as NGC 3766 (McSwain 2008). Also, while ~20% of the sample consists of known binaries, we find that another 15-30% of the sample shows indications of binarity. © International Astronomical Union 2011
Multiwavelength Observations of the Runaway Binary HD 15137
HD 15137 is an intriguing runaway O-type binary system that offers a rare
opportunity to explore the mechanism by which it was ejected from the open
cluster of its birth. Here we present recent blue optical spectra of HD 15137
and derive a new orbital solution for the spectroscopic binary and physical
parameters of the O star primary. We also present the first XMM-Newton
observations of the system. Fits of the EPIC spectra indicate soft, thermal
X-ray emission consistent with an isolated O star. Upper limits on the
undetected hard X-ray emission place limits on the emission from a proposed
compact companion in the system, and we rule out a quiescent neutron star in
the propellor regime or a weakly accreting neutron star. An unevolved secondary
companion is also not detected in our optical spectra of the binary, and it is
difficult to conclude that a gravitational interaction could have ejected this
runaway binary with a low mass optical star. HD 15137 may contain an elusive
neutron star in the ejector regime or a quiescent black hole with conditions
unfavorable for accretion at the time of our observations.Comment: Accepted to A
The Orbits of the Gamma-ray Binaries LS I +61 303 and LS 5039
LS I +61 303 and LS 5039 are two of only a handful of known high mass X-ray
binaries (HMXBs) that exhibit very high energy emission in the MeV-TeV range,
and these "gamma-ray binaries" are of renewed interest due to the recent launch
of the Fermi Gamma-ray Space Telescope. Here we present new radial velocities
of both systems based on recent red and blue optical spectra. Both systems have
somewhat discrepant orbital solutions available in the literature, and our new
measurements result in improved orbital elements and resolve the disagreements.
The improved geometry of each orbit will aid in studies of the high energy
emission region near each source.Comment: Accepted to ApJ, 13 pages, preprint2 styl
CMB-S4 Science Book, First Edition
This book lays out the scientific goals to be addressed by the
next-generation ground-based cosmic microwave background experiment, CMB-S4,
envisioned to consist of dedicated telescopes at the South Pole, the high
Chilean Atacama plateau and possibly a northern hemisphere site, all equipped
with new superconducting cameras. CMB-S4 will dramatically advance cosmological
studies by crossing critical thresholds in the search for the B-mode
polarization signature of primordial gravitational waves, in the determination
of the number and masses of the neutrinos, in the search for evidence of new
light relics, in constraining the nature of dark energy, and in testing general
relativity on large scales
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead