45 research outputs found
Fundamental Parameters of 4 Massive Eclipsing Binaries in Westerlund 1
Westerlund 1 is one of the most massive young clusters known in the Local
Group, with an age of 3-5 Myr. It contains an assortment of rare evolved
massive stars, such as blue, yellow and red supergiants, Wolf-Rayet stars, a
luminous blue variable, and a magnetar, as well as 4 massive eclipsing binary
systems (Wddeb, Wd13, Wd36, WR77o, see Bonanos 2007). The eclipsing binaries
present a rare opportunity to constrain evolutionary models of massive stars,
the distance to the cluster and furthermore, to determine a dynamical lower
limit for the mass of a magnetar progenitor. Wddeb, being a detached system, is
of great interest as it allows determination of the masses of 2 of the most
massive unevolved stars in the cluster. We have analyzed spectra of all 4
eclipsing binaries, taken in 2007-2008 with the 6.5 meter Magellan telescope at
Las Campanas Observatory, Chile, and present fundamental parameters (masses,
radii) for their component stars.Comment: 2 pages, to appear in the proceedings of the IAUS 272 on "Active OB
stars: structure, evolution, mass loss and critical limits" (Paris, July
19-23, 2010), Cambridge University Press. Editors C. Neiner, G. Wade, G.
Meynet and G. Peter
Variability of Young Massive Stars in the Arches Cluster
We present preliminary results of the first near-infrared variability study
of the Arches cluster, using adaptive optics data from NIRI/Gemini and
NACO/VLT. The goal is to discover eclipsing binaries in this young (2.5 +- 0.5
Myr), dense, massive cluster for which we will determine accurate fundamental
parameters with subsequent spectroscopy. Given that the Arches cluster contains
more than 200 Wolf-Rayet and O-type stars, it provides a rare opportunity to
determine parameters for some of the most massive stars in the Galaxy.Comment: 2 pages, to appear in the proceedings of the IAUS 272 on "Active OB
stars: structure, evolution, mass loss and critical limits" (Paris, July
19-23, 2010), Cambridge University Press. Editors C. Neiner, G. Wade, G.
Meynet and G. Peter
Variability of Young Massive Stars in the Galactic Super Star Cluster Westerlund 1
This paper presents the first optical variability study of the Westerlund 1
super star cluster in search of massive eclipsing binary systems. A total of
129 new variable stars have been identified, including the discovery of 4
eclipsing binaries that are cluster members, 1 additional candidate, 8 field
binaries, 19 field delta Scuti stars, 3 field W UMa eclipsing binaries, 13
other periodic variables and 81 long period or non-periodic variables. These
include the known luminous blue variable, the B[e] star, 11 Wolf-Rayet stars,
several supergiants, and other reddened stars that are likely members of
Westerlund 1. The bright X-ray source corresponding to the Wolf-Rayet star
WR77o (B) is found to be a 3.51 day eclipsing binary. The discovery of a
reddened detached eclipsing binary system implies the first identification of
main-sequence stars in Westerlund 1.Comment: 28 pages, 9 figures, 3 tables; accepted for publication in The
Astronomical Journal. Full-resolution version and color image of the cluster
are available at http://www.dtm.ciw.edu/bonanos/Westerlund
Techniques for Observing Binaries in Other Galaxies
I present an overview of the techniques used for detecting and following up
binaries in nearby galaxies and present the current census of extragalactic
binaries, with a focus on eclipsing systems. The motivation for looking in
other galaxies is the use of eclipsing binaries as distance indicators and as
probes of the most massive stars.Comment: 5 pages, 1 table, to appear in the proceedings of the IAUS 282 on
"From Interacting Binaries to Exoplanets: Essential Modelling Tools"
(Tatranska Lomnica, Slovakia, July 2011), Cambridge University Pres
Eclipsing Binaries: Tools for Calibrating the Extragalactic Distance Scale
In the last decade, over 7000 eclipsing binaries have been discovered in the
Local Group through various variability surveys. Measuring fundamental
parameters of these eclipsing binaries has become feasible with 8 meter class
telescopes, making it possible to use eclipsing binaries as distance
indicators. Distances with eclipsing binaries provide an independent method for
calibrating the extragalactic distance scale and thus determining the Hubble
constant. This method has been used for determining distances to eclipsing
binaries in the Magellanic Clouds and the Andromeda Galaxy and most recently to
a detached eclipsing binary in the Triangulum Galaxy by the DIRECT Project. The
increasing number of eclipsing binaries found by microlensing and variability
surveys also provide a rich database for advancing our understanding of star
formation and evolution.Comment: Review in proceedings of IAU Symposium 240, Editors W. Hartkopf, E.
Guinan & P. Harmanec; 10 page
A High-Resolution Multiband Survey of Westerlund 2 With the Hubble Space Telescope I: Is the Massive Star Cluster Double?
We present first results from a high resolution multi-band survey of the
Westerlund 2 region with the Hubble Space Telescope. Specifically, we imaged
Westerlund 2 with the Advanced Camera for Surveys through the , ,
and filters and with the Wide Field Camera 3 in the , ,
and filters. We derive the first high resolution pixel-to-pixel map of
the color excess of the gas associated with the cluster, combining
the H () and Pa () line observations. We
demonstrate that, as expected, the region is affected by significant
differential reddening with a median of ~mag. After separating
the populations of cluster members and foreground contaminants using a
vs. color-magnitude diagram, we identify a pronounced
pre-main-sequence population in Westerlund 2 showing a distinct turn-on. After
dereddening each star of Westerlund 2 individually in the color-magnitude
diagram we find via over-plotting PARSEC isochrones that the distance is in
good agreement with the literature value of ~kpc. With
zero-age-main-sequence fitting to two-color-diagrams, we derive a value of
total to selective extinction of . A spatial density map of
the stellar content reveals that the cluster might be composed of two clumps.
We estimate the same age of 0.5-2.0 Myr for both clumps. While the two clumps
appear to be coeval, the northern clump shows a lower stellar
surface density.Comment: 24 pages, 27 figures, 7 tables; Accepted for publication to The
Astronomical Journa
Towards an Accurate Determination of Parameters for Very Massive Stars: the Eclipsing Binary LMC-SC1-105
This paper presents a photometric and spectroscopic study of the bright blue
eclipsing binary LMC-SC1-105, selected from the OGLE catalog as a candidate
host of very massive stars (>=30Mo). The system is found to be a double-lined
spectroscopic binary, which indeed contains massive stars. The masses and radii
of the components are M1= 30.9+/-1.0 Mo, M2= 13.0+/-0.7 Mo, and R1= 15.1+/-0.2
Ro, R2= 11.9+/-0.2 Ro, respectively. The less massive star is found to be
filling its Roche lobe, indicating the system has undergone mass-transfer. The
spectra of LMC-SC1-105 display the Struve-Sahade effect, with the HeI lines of
the secondary appearing stronger when it is receding and causing the spectral
types to change with phase (O8+O8 to O7+O8.5). This effect could be related to
the mass-transfer in this system. To date, accurate (<=10%) fundamental
parameters have only been measured for 15 stars with masses greater than 30 Mo,
with the reported measurements contributing valuable data on the fundamental
parameters of very massive stars at low metallicity. The results of this work
demonstrate that the strategy of targeting the brightest blue stars in
eclipsing binaries is an effective way of studying very massive stars.Comment: 32 pages, 13 figures, 5 tables; accepted for publication in The
Astrophysical Journa
Low Metallicity Indicates that the Hypervelocity Star HE 0437-5439 was Ejected from the LMC
We measure the metallicity of the unusual hypervelocity star HE 0437-5439
from high resolution spectroscopy to be half-solar. We determine a spectral
type of B2 IV-III for the star and derive an effective temperature Teff= 21,500
+/- 1,000 K and a surface gravity log(g) = 3.7 +/- 0.2 (cgs). We also present
BV time series photometry and find the star to be non-variable at the 0.02 mag
level. We refine the magnitude of the hypervelocity star to V=16.36+/-0.04 mag,
with a color B-V=-0.23+/-0.03 mag, confirming its early-type nature. Our
metallicity result establishes the origin of HE 0437-5439 in the Large
Magellanic Cloud and implies the existence of a massive black hole somewhere in
this galaxy.Comment: 12 pages, 3 figures, 1 table; accepted to ApJL. Added 2 coauthors &
full abundance analysis. Results are strengthene