126 research outputs found
Predicting Stellar Angular Diameters from , , , Photometry
Determining the physical properties of microlensing events depends on having
accurate angular sizes of the source star. Using long-baseline optical
interferometry we are able to measure the angular sizes of nearby stars with
uncertainties . We present empirically derived relations of angular
diameters that are calibrated using both a sample of dwarfs/subgiants and a
sample of giant stars. These relations are functions of five color indices in
the visible and near-infrared, and have uncertainties of 1.8-6.5% depending on
the color used. We find that a combined sample of both main-sequence and
evolved stars of A-K spectral types is well fit by a single relation for each
color considered. We find that in the colors considered, metallicity does not
play a statistically significant role in predicting stellar size, leading to a
means of predicting observed sizes of stars from color alone.Comment: 8 pages, 1 figure, accepted for publication in MNRA
The full spectral radiative properties of Proxima Centauri
The discovery of Proxima b, a terrestrial temperate planet, presents the
opportunity of studying a potentially habitable world in optimal conditions. A
key aspect to model its habitability is to understand the radiation environment
of the planet in the full spectral domain. We characterize the X-rays to mid-IR
radiative properties of Proxima with the goal of providing the
top-of-atmosphere fluxes on the planet. We also aim at constraining the
fundamental properties of the star. We employ observations from a large number
of facilities and make use of different methodologies to piece together the
full spectral energy distribution of Proxima. In the high-energy domain, we pay
particular attention to the contribution by rotational modulation, activity
cycle, and flares so that the data provided are representative of the overall
radiation dose received by the atmosphere of the planet. We present the full
spectrum of Proxima covering 0.7 to 30000 nm. The integration of the data shows
that the top-of-atmosphere average XUV irradiance on Proxima b is 0.293 W m^-2,
i.e., nearly 60 times higher than Earth, and that the total irradiance is
877+/-44 W m^-2, or 64+/-3% of the solar constant but with a significantly
redder spectrum. We also provide laws for the XUV evolution of Proxima
corresponding to two scenarios. Regarding the fundamental properties of
Proxima, we find M=0.120+/-0.003 Msun, R=0.146+/-0.007 Rsun, Teff=2980+/-80 K,
and L=0.00151+/-0.00008 Lsun. In addition, our analysis reveals a ~20% excess
in the 3-30 micron flux of the star that is best interpreted as arising from
warm dust in the system. The data provided here should be useful to further
investigate the current atmospheric properties of Proxima b as well as its past
history, with the overall aim of firmly establishing the habitability of the
planet.Comment: 12 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Stellar diameters and temperatures. IV. Predicting stellar angular diameters
The number of stellar angular diameter measurements has greatly increased over the past few years due to innovations and developments in the field of long baseline optical interferometry. We use a collection of high-precision angular diameter measurements for nearby, main-sequence stars to develop empirical relations that allow the prediction of stellar angular sizes as a function of observed photometric color. These relations are presented for a combination of 48 broadband color indices. We empirically show for the first time a dependence on metallicity of these relations using Johnson (B-V) and Sloan (g-r) colors. Our relations are capable of predicting diameters with a random error of less than 5% and represent the most robust and empirical determinations of stellar angular sizes to date. © 2014. The American Astronomical Society. All rights reserved.
A New Analysis of the Exoplanet Hosting System HD 6434
The current goal of exoplanetary science is not only focused on detecting but
characterizing planetary systems in hopes of understanding how they formed,
evolved, and relate to the Solar System. The Transit Ephemeris Refinement and
Monitoring Survey (TERMS) combines both radial velocity (RV) and photometric
data in order to achieve unprecedented ground-based precision in the
fundamental properties of nearby, bright, exoplanet-hosting systems. Here we
discuss HD 6434 and its planet, HD 6434b, which has a M_p*sin(i) = 0.44 M_J
mass and orbits every 22.0170 days with an eccentricity of 0.146. We have
combined previously published RV data with new measurements to derive a
predicted transit duration of ~6 hrs, or 0.25 days, and a transit probability
of 4%. Additionally, we have photometrically observed the planetary system
using both the 0.9m and 1.0m telescopes at the Cerro Tololo Inter-American
Observatory, covering 75.4% of the predicted transit window. We reduced the
data using the automated TERMS Photometry Pipeline, developed to ensure
consistent and accurate results. We determine a dispositive null result for the
transit of HD 6434b, excluding the full transit to a depth of 0.9% and grazing
transit due to impact parameter limitations to a depth of 1.6%Comment: 9 pages, 5 figures, 3 tables, accepted to A
The ejection of runaway massive binaries
The runaway O-type stars HD 14633 and HD 15137 are both SB1 systems that were probably ejected from the open cluster NGC 654. Were these stars dynamically ejected by close gravitational encounters in the dense cluster, or did the binaries each receive a kick from a supernova in one member? We present new results from our investigation of the optical, X-ray, and radio properties of these binary systems to discuss the probable ejection scenarios. We argue that these binaries may have been ejected via dynamical interactions in the dense cluster environment. © 2007 International Astronomical Union
KIC 9406652: An Unusual Cataclysmic Variable in the Kepler Field of View
KIC 9406652 is a remarkable variable star in the Kepler field of view that
shows both very rapid oscillations and long term outbursts in its light curve.
We present an analysis of the light curve over quarters 1 to 15 and new
spectroscopy that indicates that the object is a cataclysmic variable with an
orbital period of 6.108 hours. However, an even stronger signal appears in the
light curve periodogram for a shorter period of 5.753 hours, and we argue that
this corresponds to the modulation of flux from the hot spot region in a
tilted, precessing disk surrounding the white dwarf star. We present a
preliminary orbital solution from radial velocity measurements of features from
the accretion disk and the photosphere of the companion. We use a Doppler
tomography algorithm to reconstruct the disk and companion spectra, and we also
consider how these components contribute to the object's spectral energy
distribution from ultraviolet to infrared wavelengths. This target offers us a
remarkable opportunity to investigate disk processes during the high mass
transfer stage of evolution in cataclysmic variables.Comment: 31 pages, 13 figures, accepted for Ap
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