65 research outputs found
Variability of Be Stars in Southern Open Clusters
We recently discovered a large number of highly active Be stars in the open
cluster NGC 3766, making it an excellent location to study the formation
mechanism of Be star disks. To explore whether similar disk appearances and/or
disappearances are common among the Be stars in other open clusters, we present
here multiple epochs of H-alpha spectroscopy for 296 stars in eight open
clusters. We identify 12 new transient Be stars and confirm 17 additional Be
stars with relatively stable disks. By comparing the H-alpha equivalent widths
to the photometric y - H-alpha colors, we present a method to estimate the
strength of the H-alpha emission when spectroscopy is not available. For a
subset of 128 stars in four open clusters, we also use blue optical
spectroscopy and available Stromgren photometry to measure their projected
rotational velocities, effective temperatures, and polar surface gravities. We
combine our Be star detections from these four clusters to investigate physical
differences between the transient Be stars, stable Be stars, and normal B-type
stars with no line emission. Both types of Be stars are faster rotating
populations than normal B-type stars, and we find no significant physical
differences between the transient and stable Be stars in our sample.Comment: Accepted to ApJ; small corrections to Table 5 and associated figure
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
Non-radial Pulsations in the Open Cluster NGC 3766
Non-radial pulsations (NRPs) are a proposed mechanism for the formation of
decretion disks around Be stars and are important tools to study the internal
structure of stars. NGC 3766 has an unusually large fraction of transient Be
stars, so it is an excellent location to study the formation mechanism of Be
star disks. High resolution spectroscopy can reveal line profile variations
from NRPs, allowing measurements of both the degree, l, and azimuthal order, m.
However, spectroscopic studies require large amounts of time with large
telescopes to achieve the necessary high S/N and time domain coverage. On the
other hand, multi-color photometry can be performed more easily with small
telescopes to measure l only. Here, we present representative light curves of
Be stars and non-emitting B stars in NGC 3766 from the CTIO 0.9m telescope in
an effort to study NRPs in this cluster.Comment: 4 pages, to appear in the proceedings of IAU Symposium 266: Star
Cluster
Multiwavelength Observations of Gamma-ray Binary Candidates
A rare group of high mass X-ray binaries (HMXBs) are known that also exhibit
MeV, GeV, and/or TeV emission ("gamma-ray binaries"). Expanding the sample of
gamma-ray binaries and identifying unknown Fermi sources are currently of great
interest to the community. Based upon their positional coincidence with the
unidentified Fermi sources 1FGL J1127.7-6244c and 1FGL J1808.5-1954c, the Be
stars HD 99771 and HD 165783 have been proposed as gamma-ray binary candidates.
During Fermi Cycle 4, we have performed multiwavelength observations of these
sources using XMM-Newton and the CTIO 1.5m telescope. We do not confirm high
energy emission from the Be stars. Here we examine other X-ray sources in the
field of view that are potential counterparts to the Fermi sources.Comment: 2012 Fermi Symposium proceedings - eConf C12102
H-alpha Emission Variability in the gamma-ray Binary LS I +61 303
LS I +61 303 is an exceptionally rare example of a high mass X-ray binary
(HMXB) that also exhibits MeV-TeV emission, making it one of only a handful of
"gamma-ray binaries". Here we present H-alpha spectra that show strong
variability during the 26.5 day orbital period and over decadal time scales. We
detect evidence of a spiral density wave in the Be circumstellar disk over part
of the orbit. The H-alpha line profile also exhibits a dramatic emission burst
shortly before apastron, observed as a redshifted shoulder in the line profile,
as the compact source moves almost directly away from the observer. We
investigate several possible origins for this red shoulder, including an
accretion disk, mass transfer stream, and a compact pulsar wind nebula that
forms via a shock between the Be star's wind and the relativistic pulsar wind.Comment: Accepted to Ap
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