98 research outputs found
Asteroseismology, standard candles and the Hubble Constant: what is the role of asteroseismology in the era of precision cosmology?
Classical Cepheids form one of the foundations of modern cosmology and the
extragalactic distance scale, however, cosmic microwave background observations
measure cosmological parameters and indirectly the Hubble Constant, H0, to
unparalleled precision. The coming decade will provide opportunities to measure
H0 to 2% uncertainty thanks to the GAIA satellite, JWST, ELTs and other
telescopes using Cepheids and other standard candles. In this work, we discuss
the upcoming role for variable stars and asteroseismology in calibrating the
distance scale and measuring H0 and what problems exist in understanding these
stars that will feedback on these measurements.Comment: 8 pages, summary of splinter session at IAU Symposium 301, Precision
Asteroseismology, August 2013, Wroclaw, Polan
Cepheid Masses: FUSE Observations of S Mus
S Mus is the Cepheid with the hottest known companion. The large ultraviolet
flux means that it is the only Cepheid companion for which the velocity
amplitude could be measured with the echelle mode of the HST GHRS.
Unfortunately, the high temperature is difficult to constrain at wavelengths
longer than 1200 \AA because of the degeneracy between temperature and
reddening. We have obtained a FUSE spectrum in order to improve the
determination of the temperature of the companion. Two regions which are
temperature sensitive near 16,000 K but relatively unaffected by H
absorption (940 \AA, and the Ly wings) have been identified. By
comparing FUSE spectra of S Mus B with spectra of standard stars, we have
determined a temperature of 17,000 500 K. The resultant Cepheid mass is
6.0 0.4 M. This mass is consistent with main sequence
evolutionary tracks with a moderate amount of convective overshoot.Comment: accepted to Ap
X-Atlas: An Online Archive of Chandra's Stellar High Energy Transmission Gratings Observations
The high-resolution X-ray spectroscopy made possible by the 1999 deployment
of the Chandra X-ray Observatory has revolutionized our understanding of
stellar X-ray emission. Many puzzles remain, though, particularly regarding the
mechanisms of X-ray emission from OB stars. Although numerous individual stars
have been observed in high-resolution, realizing the full scientific potential
of these observations will necessitate studying the high-resolution Chandra
dataset as a whole. To facilitate the rapid comparison and characterization of
stellar spectra, we have compiled a uniformly processed database of all stars
observed with the Chandra High Energy Transmission Grating (HETG). This
database, known as X-Atlas, is accessible through a web interface with
searching, data retrieval, and interactive plotting capabilities. For each
target, X-Atlas also features predictions of the low-resolution ACIS spectra
convolved from the HETG data for comparison with stellar sources in archival
ACIS images. Preliminary analyses of the hardness ratios, quantiles, and
spectral fits derived from the predicted ACIS spectra reveal systematic
differences between the high-mass and low-mass stars in the atlas and offer
evidence for at least two distinct classes of high-mass stars. A high degree of
X-ray variability is also seen in both high and low-mass stars, including
Capella, long thought to exhibit minimal variability. X-Atlas contains over 130
observations of approximately 25 high-mass stars and 40 low-mass stars and will
be updated as additional stellar HETG observations become public. The atlas has
recently expanded to non-stellar point sources, and Low Energy Transmission
Grating (LETG) observations are currently being added as well
High Mass Triple Systems: The Classical Cepheid Y Car
We have obtained an HST STIS ultraviolet high dispersion Echelle mode
spectrum the binary companion of the double mode classical Cepheid Y Car. The
velocity measured for the hot companion from this spectrum is very different
from reasonable predictions for binary motion, implying that the companion is
itself a short period binary. The measured velocity changed by 7 km/ s during
the 4 days between two segments of the observation confirming this
interpretation. We summarize "binary" Cepheids which are in fact members of
triple system and find at least 44% are triples. The summary of information on
Cepheids with orbits makes it likely that the fraction is under-estimated.Comment: accepted by A
The Search for Low-mass Companions of B Stars in the Carina Nebula Cluster Trumpler 16
We have developed lists of likely B3--A0 stars (called "late B" stars) in the
young cluster Trumpler 16. The following criteria were used: location within 3'
of Eta Car, an appropriate V and B-V combination, and proper motion (where
available). Color and magnitude cuts have been made assuming an E(B-V) =0.55
mag +/- 0.1, which is a good approximation close to the center of Trumpler 16.
These lists have been cross-correlated with X-ray sources found in the Chandra
Carina Complex Project (CCCP). Previous studies have shown that only very
rarely (if at all) do late main sequence B stars produce X-rays. We present
evidence that the X-ray detected sources are binaries with low-mass companions,
since stars less massive than 1.4 Msun are strong X-ray sources at the age of
the cluster. Both the median X-ray energies and X-ray luminosities of these
sources are in good agreement with values for typical low-mass coronal X-ray
sources. We find that 39% of the late B stars based on a list with proper
motions have low-mass companions. Similarly, 32% of a sample without proper
motions have low-mass companions. We discuss the X-ray detection completeness.
These results on low-mass companions of intermediate mass stars are
complementary to spectroscopic and interferometric results, and probe new
parameter space of low mass companions at all separations. They do not support
a steeply rising distribution of mass ratios to low masses for
intermediate-mass (5 Msun) primaries, such as would be found by random pairing
from the Initial Mass Function.Comment: Accepted for the ApJS Special Issue on the Chandra Carina Complex
Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special
Issue papers are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at
leas
Socially-mediated arousal and contagion within domestic chick broods
Emotional contagion – an underpinning valenced feature of empathy – is made up of simpler, potentially dissociable social processes which can include socially-mediated arousal and behavioural/physiological contagion. Previous studies of emotional contagion have often conflated these processes rather than examining their independent contribution to empathic response. We measured socially-mediated arousal and contagion in 9-week old domestic chicks (n = 19 broods), who were unrelated but raised together from hatching. Pairs of observer chicks were exposed to two conditions in a counterbalanced order: air puff to conspecifics (AP) (during which an air puff was applied to three conspecifics at 30 s intervals) and control with noise of air puff (C) (during which the air puff was directed away from the apparatus at 30 s intervals). Behaviour and surface eye temperature of subjects and observers were measured throughout a 10-min pre-treatment and 10-min treatment period. Subjects and observers responded to AP with increased freezing, and reduced preening and ground pecking. Subjects and observers also showed reduced surface eye temperature - indicative of stress-induced hyperthermia. Subject-Observer behaviour was highly correlated within broods during both C and AP conditions, but with higher overall synchrony during AP. We demonstrate the co-occurrence of socially-mediated behavioural and physiological arousal and contagion; component features of emotional contagion
Carina OB Stars: X-ray Signatures of Wind Shocks and Magnetic Fields
The Chandra Carina Complex contains 200 known O- and B type stars. The
Chandra survey detected 68 of the 70 O stars and 61 of 127 known B0-B3 stars.
We have assembled a publicly available optical/X-ray database to identify OB
stars that depart from the canonical Lx/Lbol relation, or whose average X-ray
temperatures exceed 1 keV. Among the single O stars with high kT we identify
two candidate magnetically confined wind shock sources: Tr16-22, O8.5 V, and LS
1865, O8.5 V((f)). The O4 III(fc) star HD 93250 exhibits strong, hard, variable
X-rays, suggesting it may be a massive binary with a period of >30 days. The
visual O2 If* binary HD 93129A shows soft 0.6 keV and hard 1.9 keV emission
components, suggesting embedded wind shocks close to the O2 If* Aa primary, and
colliding wind shocks between Aa and Ab. Of the 11 known O-type spectroscopic
binaries, the long orbital-period systems HD 93343, HD 93403 and QZ Car have
higher shock temperatures than short-period systems such as HD 93205 and FO 15.
Although the X-rays from most B stars may be produced in the coronae of unseen,
low-mass pre-main-sequence companions, a dozen B stars with high Lx cannot be
explained by a distribution of unseen companions. One of these, SS73 24 in the
Treasure Chest cluster, is a new candidate Herbig Be star.Comment: To be published in a special issue of the Astrophysical Journal
Supplement on the Chandra Carina Complex Projec
An Introduction to the Chandra Carina Complex Project
The Great Nebula in Carina provides an exceptional view into the violent
massive star formation and feedback that typifies giant HII regions and
starburst galaxies. We have mapped the Carina star-forming complex in X-rays,
using archival Chandra data and a mosaic of 20 new 60ks pointings using the
Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for
understanding recent and ongoing star formation and to probe Carina's regions
of bright diffuse X-ray emission. This study has yielded a catalog of
properties of >14,000 X-ray point sources; >9800 of them have multiwavelength
counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have
separated these point sources from the extensive, spatially-complex diffuse
emission that pervades the region; X-ray properties of this diffuse emission
suggest that it traces feedback from Carina's massive stars. In this
introductory paper, we motivate the survey design, describe the Chandra
observations, and present some simple results, providing a foundation for the
15 papers that follow in this Special Issue and that present detailed catalogs,
methods, and science results.Comment: Accepted for the ApJS Special Issue on the Chandra Carina Complex
Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special
Issue papers are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at
least. 43 pages; 18 figure
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