274 research outputs found
On the Binary Nature of Dust-encircled BD+20 307
Three epochs of high resolution spectra of the star BD+20 307 show that it is
a short period (~3.5 day) spectroscopic binary of two nearly identical stars.
Surprisingly, the two stars, though differing in effective temperature by only
~250 K and having a mass ratio of 0.91, show very different Li line equivalent
widths. A Li 6707 Angstrom line is only detected from the primary star, and it
is weak. This star is therefore likely to be older than 1 Gyr. If so, the large
amount of hot circumbinary dust must be from a very large and recent, but very
late evolutionarily, collision of planetesimals.Comment: Accepted to ApJ Letters, with corrected typos and added info on Li
equivalent width
The XO Planetary Survey Project - Astrophysical False Positives
Searches for planetary transits find many astrophysical false positives as a
by-product. There are four main types analyzed in the literature: a
grazing-incidence eclipsing binary star, an eclipsing binary star with a small
radius companion star, a blend of one or more stars with an unrelated eclipsing
binary star, and a physical triple star system. We present a list of 69
astrophysical false positives that had been identified as candidates of
transiting planets of the on-going XO survey. This list may be useful in order
to avoid redundant observation and characterization of these particular
candidates independently identified by other wide-field searches for transiting
planets. The list may be useful for those modeling the yield of the XO survey
and surveys similar to it. Subsequent observations of some of the listed stars
may improve mass-radius relations, especially for low-mass stars. From the
candidates exhibiting eclipses, we report three new spectroscopic double-line
binaries and give mass function estimations for 15 single lined spectroscopic
binaries.Comment: 13 pages, 4 figures, accepted to ApJ
Five More Massive Binaries in the Cygnus OB2 Association
We present the orbital solutions for four OB spectroscopic binaries, MT145,
GSC 03161-00815, 2MASS J20294666+4105083, and Schulte 73, and the partial
orbital solution to the B spectroscopic binary, MT372, as part of an ongoing
study to determine the distribution of orbital parameters for massive binaries
in the Cygnus OB2 Association. MT145 is a new, single-lined, moderately
eccentric (e=0.291+/-0.009) spectroscopic binary with period of 25.140+/-0.008
days. GSC 03161-00815 is a slightly eccentric (e=0.10+/-0.01), eclipsing,
interacting and double-lined spectroscopic binary with a period of
4.674+/-0.004 days. 2MASS J20294666+4105083 is a moderately eccentric
(e=0.273+/-0.002) double-lined spectroscopic binary with a period of
2.884+/-0.001 days. Schulte 73 is a slightly eccentric (e=0.169+/-0.009),
double-lined spectroscopic binary with a period of 17.28+/-0.03 days and the
first "twin" in our survey with a mass ratio of q=0.99+/-0.02. MT372 is a
single-lined, eclipsing system with a period of 2.228 days and low eccentricity
(e~0). Of the now 18 known OB binaries in Cyg OB2, 14 have periods and mass
ratios. Emerging evidence also shows that the distribution of log(P) is flat
and consistent with Oepik's Law.Comment: Accepted to Astronomical Journa
Feasibility of an Infrared Parallax Program Using the Fan Mountain Tinsley Reflector
Despite the continuing importance of ground-based parallax measurements, few
active programs remain. Because new members of the solar neighborhood tend
towards later spectral types, infrared parallax programs are particularly
desirable. Consequently, the astrometric quality of the new infrared camera,
FanCam, developed by the Virginia Astronomical Instrumentation Laboratory
(VAIL) for the 31-in (0.8-m) Tinsley reflector at Fan Mountain Observatory was
assessed using 68 J-band exposures of an open cluster, NGC 2420, over a range
of hour angles during 2005. Positions of 16 astrometric evaluation stars were
measured and the repeatability of those positions was evaluated using the mean
error in a single observation of unit weight. Overall, a precision of 1.3 +/-
0.7 microns in x (RA) and 1.3 +/- 0.8 microns in y (Dec) was attained, which
corresponds to 0.04" +/- 0.02" in each axis. Although greater precision is
expected from CCDs in the visual and near-infrared, this instrument can achieve
precision similar to that of the ESO NTT infrared parallax program. Therefore,
measuring parallaxes in the infrared would be feasible using this equipment. If
initiated, such a program could provide essential distances for brown dwarfs
and very low mass stars that would contribute significantly to the solar
neighborhood census.Comment: accepted by New Astronomy, minor revisions per refere
Discovery of New, Dust-Poor B[e] Supergiants in the Small Magellanic Cloud
We present the discovery of three new B[e] supergiants (sgB[e] stars) in the
Small Magellanic Cloud (SMC). All three stars (R15, R38, and R48) were
identified in the course of our Runaways and Isolated O Type Star Spectroscopic
Survey of the SMC (RIOTS4). The stars show optical spectra that closely
resemble those of previously known B[e] stars, presenting numerous
low-ionization forbidden and permitted emission lines such as [Fe II] and Fe
II. Furthermore, our stars have luminosities of log(L/L_sun) > 4, demonstrating
that they are supergiants. However, we find lower infrared excesses and weaker
forbidden emission lines than for previously identified B[e] supergiants. Thus
our stars appear to either have less material in their circumstellar disks than
other sgB[e] stars, or the circumstellar material has lower dust content. We
suggest that these may constitute a new subclass of dust-poor sgB[e] stars.Comment: 7 pages, 6 figures, accepted to Ap
Sh2-205: II. Its quiescent stellar formation activity
We present a study of active stellar forming regions in the environs of the
HII region Sh2-205. The analysis is based on data obtained from point source
catalogues and images extracted from 2MASS, MSX, and IRAS surveys.
Complementary data are taken from CO survey. The identification of primary
candidates to stellar formation activity is made following colour criteria and
the correlation with molecular gas emission.
A number of stellar formation tracer candidates are projected on two
substructures of the HII region: SH148.83-0.67 and SH149.25-0.00. However, the
lack of molecular gas related to these structures casts doubts on the nature of
the sources. Additional infrared sources may be associated with the HI shell
centered at (l,b) = (149\degr 0\arcmin, -1\degr 30\arcmin).
The most striking active area was found in connection to the HII region LBN
148.11-0.45, where stellar formation candidates are projected onto molecular
gas. The analytical model to the "collect and collapse" process shows that
stellar formation activity could have been triggered by the expansion of this
HII region.Comment: Accepted for publication in MNRAS, 10 pages, 5 figures, 5 table
Cool bottom processes on the thermally-pulsing AGB and the isotopic composition of circumstellar dust grains
(Abridged) We examine the effects of cool bottom processing (CBP) on several
isotopic ratios in the convective envelope during the TP-AGB phase of evolution
in a 1.5 M_sun initial-mass star of solar initial composition. We use a
parametric model which treats extra mixing by introducing mass flow between the
convective envelope and the underlying radiative zone. The parameters of this
model are the mass circulation rate (Mdot) and the maximum temperature (T_P)
experienced by the circulating material. The effects of nuclear reactions in
the flowing matter were calculated using a set of structures of the radiative
zone selected from a complete stellar evolution calculation. The compositions
of the flowing material were obtained and the resulting changes in the envelope
determined. Abundant ^26Al was produced by CBP for log T_P > 7.65. While
^26Al/^27Al depends on T_P, the isotopic ratios in CNO elements depend
dominantly on the circulation rate. The correspondence is shown between models
of CBP as parameterized by a diffusion formalism within the stellar evolution
model and those using the mass-flow formalism employed here. The isotopic
ratios are compared with the data on circumstellar dust grains. It is found
that the ratios ^{18}O/^{16}O, ^{17}O/^{16}O, and ^26Al/^27Al observed for
oxide grains formed at C/O < 1 are reasonably well-understood. However, the
^15N/^14N, ^12C/^13C, and ^26Al/^27Al in carbide grains (C/O > 1) require many
stellar sources with ^14N/^15N at least a factor of 4 below solar. The rare
grains with ^12C/^13C < 10 cannot be produced by any red-giant or AGB source.Comment: 35 pages, plus 18 included figures. Scheduled for January 10, 2003
issue of Ap
Abundances in HD27411 and the helium problem in Am stars
We analyze a high-resolution spectrum of the A3m star HD27411. We compare
abundances derived from ATLAS9 model atmospheres with those using the more
computationally-intensive ATLAS12 code. We found very little differences in the
abundances, suggesting that ATLAS9 can be used for moderate chemical
peculiarity. Our abundances agree well with the predictions of diffusion
theory, though for some elements it was necessary to calculate line profiles in
non-thermodynamic equilibrium to obtain agreement. We investigate the effective
temperatures and luminosities of Am/Fm stars using synthetic Stromgren indices
derived from calculated spectra with the atmospheric abundances of HD27411. We
find that the effective temperatures of Am/Fm stars derived from Stromgren
photometry are reliable, but the luminosities are probably too low. Caution is
required when deriving the reddening of these stars owing to line blanketing
effects. A comparison of the relative proportions of pulsating and
non-pulsating Am stars with delta Scuti stars shows quite clearly that there is
no significant decrease of helium in the driving zone, contrary to current
models of diffusion.Comment: 10 pages, 8 figures, 6 tables, accepted for publication in MNRA
NSVS06507557; a low-mass double-lined eclipsing binary
In this paper we present the results of a detailed spectroscopic and
photometric analysis of the V=13.4 low-mass eclipsing binary NSVS 06507557
with an orbital period of 0.515 d. We obtained a series of mid-resolution
spectra covering nearly entire orbit of the system. In addition we obtained
simultaneous VRI broadband photometry using a small aperture telescope. From
these spectroscopic and photometric data we have derived the system's orbital
parameters and determined the fundamental stellar parameters of the two
components. Our results indicate that NSVS 06507557 consists of a K9 and an M3
pre-main-sequence stars with masses of 0.660.09 \Msun and 0.280.05
\Msun and radii of 0.600.03 and 0.440.02 \Rsun, located at a distance
of 1119 pc. The radius of the less massive secondary component is larger
than that of the zero-age main-sequnce star having the same mass. While the
radius of the primary component is in agreement with ZAMS the secondary
component appers to be larger by about 35 % with respect to its ZAMS
counterpart. Night-to-night intrinsic light variations up to 0.2 have been
observed. In addition, the H, H lines and the forbidden
line of [O{\sc i}] are seen in emission. The Li{\sc i} 6708 \AA absorption line
is seen in most of the spectra. These features are taken to be the signs of the
classic T Tauri stars' characteristics. The parameters we derived are
consistent with an age of about 20 Myr according to the stellar evolutionary
models. The spectroscopic and photometric results are in agreement with those
obtained by theoretical predictions.Comment: 21 pages, 9 figures. Accepted by MNRA
Reduced innate immune response to a Staphylococcus aureus small colony variant compared to its wild-type parent strain
Background: Staphylococcus aureus (S. aureus) small colony variants (SCVs) can survive within the host intracellular milieu and are associated with chronic relapsing infections. However, it is unknown whether host invasion rates and immune responses differ between SCVs and their wild-type counterparts. This study used a stable S. aureus SCV (WCH-SK2SCV) developed from a clinical isolate (WCH-SK2WT) in inflammation-relevant conditions. Intracellular infection rates as well as host immune responses to WCH-SK2WT and WCH-SK2SCV infections were investigated. Method: NuLi-1 cells were infected with either WCH-SK2WT or WCH-SK2SCV, and the intracellular infection rate was determined over time. mRNA expression of cells infected with each strain intra- and extra-cellularly was analyzed using a microfluidic qPCR array to generate an expression profile of thirty-nine genes involved in the host immune response. Results: No difference was found in the intracellular infection rate between WCH-SK2WT and WCH-SK2SCV. Whereas, extracellular infection induced a robust pro-inflammatory response, intracellular infection elicited a modest response. Intracellular WCH-SK2WT infection induced mRNA expression of TLR2, pro-inflammatory cytokines (IL1B, IL6, and IL12) and tissue remodeling factors (MMP9). In contrast, intracellular WCH-SK2SCV infection induced up regulation of only TLR2. Conclusions: Whereas, host intracellular infection rates of WCH-SK2SCV and WCH-SK2WT were similar, WCH-SK2SCV intracellular infection induced a less widespread up regulation of pro-inflammatory and tissue remodeling factors in comparison to intracellular WCH-SK2WT infection. These findings support the current view that SCVs are able to evade host immune detection to allow their own survival.Judy J.J. Ou, Amanda J. Drilling, Clare Cooksley, Ahmed Bassiouni, Stephen P. Kidd, Alkis J. Psaltis, Peter J. Wormald and Sarah Vreugd
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