483 research outputs found
The fundamental parameters of the roAp star 10 Aql
Due to the strong magnetic field and related abnormal surface layers existing
in rapidly oscillating Ap stars, systematic errors are likely to be present
when determining their effective temperatures, which potentially compromises
asteroseismic studies of these pulsators. Using long-baseline interferometry,
our goal is to determine accurate angular diameters of a number of roAp targets
to provide a temperature calibration for these stars. We obtained
interferometric observations of 10 Aql with the visible spectrograph VEGA at
the CHARA array. We determined a limb-darkened angular diameter of
0.275+/-0.009 mas and deduced a linear radius of 2.32+/-0.09 R_sun. We
estimated the star's bolometric flux and used it, in combination with its
parallax and angular diameter, to determine the star's luminosity and effective
temperature. For two data sets of bolometric flux we derived an effective
temperature of 7800+/-170 K and a luminosity of 18+/-1 L_sun or of 8000+/-210 K
and 19+/-2 L_sun. We used these fundamental parameters together with the large
frequency separation to constrain the mass and the age of 10 Aql, using the
CESAM stellar evolution code. Assuming a solar chemical composition and
ignoring all kinds of diffusion and settling of elements, we obtained a mass of
1.92 M_sun and an age of 780 Gy or a mass of 1.95 M_sun and an age of 740 Gy,
depending on the considered bolometric flux. For the first time, we managed to
determine an accurate angular diameter for a star smaller than 0.3 mas and to
derive its fundamental parameters. In particular, by only combining our
interferometric data and the bolometric flux, we derived an effective
temperature that can be compared to those derived from atmosphere models. Such
fundamental parameters can help for testing the mechanism responsible for the
excitation of the oscillations observed in the magnetic pulsating stars
Fundamental Properties of Cool Stars with Interferometry
We present measurements of fundamental astrophysical properties of nearby,
low-mass, K- and M-dwarfs from our DISCOS survey (DIameterS of COol Stars). The
principal goal of our study is the determination of linear radii and effective
temperatures for these stars. We calculate their radii from angular diameter
measurements using the CHARA Array and Hipparcos distances. Combined with
bolometric flux measurements based on literature photometry, we use our angular
diameter results to calculate their effective surface temperatures. We present
preliminary results established on an assortment of empirical relations to the
stellar effective temperature and radius that are based upon these
measurements. We elaborate on the discrepancy seen between theoretical and
observed stellar radii, previously claimed to be related to stellar activity
and/or metallicity. Our preliminary conclusion, however, is that convection
plays a larger role in the determination of radii of these late-type stars.
Understanding the source of the radius disagreement is likely to impact other
areas of study for low-mass stars, such as the detection and characterization
of extrasolar planets in the habitable zones.Comment: Contribution to Proceedings of Cool Stars 16 Workshop; 8 pages in ASP
format; 9 figure
Searching for keV Sterile Neutrino Dark Matter with X-ray Microcalorimeter Sounding Rockets
High-resolution X-ray spectrometers onboard suborbital sounding rockets can
search for dark matter candidates that produce X-ray lines, such as decaying
keV-scale sterile neutrinos. Even with exposure times and effective areas far
smaller than XMM-Newton and Chandra observations, high-resolution, wide
field-of-view observations with sounding rockets have competitive sensitivity
to decaying sterile neutrinos. We analyze a subset of the 2011 observation by
the X-ray Quantum Calorimeter instrument centered on Galactic coordinates l =
165, b = -5 with an effective exposure of 106 seconds, obtaining a limit on the
sterile neutrino mixing angle of sin^2(2 theta) < 7.2e-10 at 95% CL for a 7 keV
neutrino. Better sensitivity at the level of sin^2(2 theta) ~ 2.1e-11 at 95\%
CL for a 7 keV neutrino is achievable with future 300-second observations of
the galactic center by the Micro-X instrument, providing a definitive test of
the sterile neutrino interpretation of the reported 3.56 keV excess from galaxy
clusters.Comment: 13 pages, 13 figures, submitted to Ap
Psychophysiologic responses to the Rorschach in PTSD patients, noncombat and combat controls
While psychophysiologic studies of posttraumatic stress disorder (PTSD) have investigated the effects of trauma-related stimuli on arousal, none have explored the development of intrusive imagery and affect states in the absence of such specific cues. The present study compares autonomic arousal during PTSD-related Rorschach responses in PTSD veterans vs. combat controls and noncombat controls. It was found that Rorschach responses containing traumatic content were found only in the PTSD group, and that these responses showed elevations in skin conductance (SC) and heart rate (HR). Our data also suggest that PTSD patients are more easily hyperaroused, especially under conditions of experienced stress and helplessness. Finally, combat control subjects exhibited lower baseline SC and HR than their counterparts, as well as decelerated HR during trauma- and stress-related Rorschach responses, suggesting a physiologic resilience in this group. Depression and Anxiety 8:112–120, 1998. © 1998 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/35216/1/3_ftp.pd
The Ages of A-Stars I: Interferometric Observations and Age Estimates for Stars in the Ursa Major Moving Group
We have observed and spatially resolved a set of seven A-type stars in the
nearby Ursa Major moving group with the Classic, CLIMB, and PAVO beam combiners
on the CHARA Array. At least four of these stars have large rotational
velocities ( 170 ) and are expected to
be oblate. These interferometric measurements, the stars' observed photometric
energy distributions, and values are used to computationally
construct model oblate stars from which stellar properties (inclination,
rotational velocity, and the radius and effective temperature as a function of
latitude, etc.) are determined. The results are compared with MESA stellar
evolution models (Paxton et al. 2011, 2013) to determine masses and ages. The
value of this new technique is that it enables the estimation of the
fundamental properties of rapidly rotating stars without the need to fully
image the star. It can thus be applied to stars with sizes comparable to the
interferometric resolution limit as opposed to those that are several times
larger than the limit. Under the assumption of coevality, the spread in ages
can be used as a test of both the prescription presented here and the MESA
evolutionary code for rapidly rotating stars. With our validated technique, we
combine these age estimates and determine the age of the moving group to be 414
23 Myr, which is consistent with, but much more precise than previous
estimates.Comment: Accepted by Ap
Empowerment and the Transition to Housing for Homeless Mentally Ill People: An Anthropological Perspective
Often lacking in scholarly and policy-oriented discussions of homelessness are contextualized understandings of the problems faced, and the values held, by homeless mentally ill people. This article, using an anthropological perspective, examines issues that arise for homeless mentally ill individuals in making the transition from shelter living to permanent residences. The transition occurs as part of a housing initiative driven by the philosophy of consumer empowerment. Project participants are placed in independent apartments or evolving consumer households (ECH) — shared, staffed residences designed to transform themselves into consumer-directed living situations over time. The effects of an empowerment paradigm on the organization of space, the nature of social relations, and the management of economic resources in the ECHs are discussed to show that consumers and staff sometimes have contrasting views of what empowerment entails. It is suggested that anthropological research can help to illuminate the issues at stake in determining policy for homeless people with major mental illness
The fundamental parameters of the roAp star Equulei
Physical processes working in the stellar interiors as well as the evolution
of stars depend on some fundamental stellar properties, such as mass, radius,
luminosity, and chemical abundances. A classical way to test stellar interior
models is to compare the predicted and observed location of a star on
theoretical evolutionary tracks in a H-R diagram. This requires the best
possible determinations of stellar mass, radius, luminosity and abundances. To
derive its fundamental parameters, we observed the well-known rapidly
oscillating Ap star, Equ, using the visible spectro-interferometer
VEGA installed on the optical CHARA array. We computed the calibrated squared
visibility and derived the limb-darkened diameter. We used the whole energy
flux distribution, the parallax and this angular diameter to determine the
luminosity and the effective temperature of the star. We obtained a
limb-darkened angular diameter of 0.564~~0.017~mas and deduced a radius of
~=~2.20~~0.12~. Without considering the multiple
nature of the system, we derived a bolometric flux of erg~cm~s and an effective temperature of
7364~~235~K, which is below the effective temperature that has been
previously determined. Under the same conditions we found a luminosity of
~=~12.8~~1.4~. When the contribution of the closest
companion to the bolometric flux is considered, we found that the effective
temperature and luminosity of the primary star can be, respectively, up to
~100~K and up to ~0.8~L smaller than the values mentioned
above.These new values of the radius and effective temperature should bring
further constraints on the asteroseismic modelling of the star.Comment: Accepted by A&
New & Noteworthy, January 2018
Contents include: Happy Lessing Week!; Q+A | Jo Jo Stiletto; Fom [sic] LMDA Regional VP Jacqueline Goldfinger; Announcments; Regional Activities.https://soundideas.pugetsound.edu/lmdanewsletter/1064/thumbnail.jp
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