418 research outputs found
Survey for Transiting Extrasolar Planets in Stellar Systems. II. Spectrophotometry and Metallicities of Open Clusters
We present metallicity estimates for seven open clusters based on
spectrophotometric indices from moderate-resolution spectroscopy. Observations
of field giants of known metallicity provide a correlation between the
spectroscopic indices and the metallicity of open cluster giants. We use \chi^2
analysis to fit the relation of spectrophotometric indices to metallicity in
field giants. The resulting function allows an estimate of the target-cluster
giants' metallicities with an error in the method of \pm0.08 dex. We derive the
following metallicities for the seven open clusters: NGC 1245,
[m/H]=-0.14\pm0.04; NGC 2099, [m/H]=+0.05\pm0.05; NGC 2324, [m/H]=-0.06\pm0.04;
NGC 2539, [m/H]=-0.04\pm0.03; NGC 2682 (M67), [m/H]=-0.05\pm0.02; NGC 6705,
[m/H]=+0.14\pm0.08; NGC 6819, [m/H]=-0.07\pm0.12. These metallicity estimates
will be useful in planning future extra-solar planet transit searches since
planets may form more readily in metal-rich environments.Comment: 38 pages, including 12 figures. Accepted for publication in A
Deep MMT Transit Survey of the Open Cluster M37 IV: Limit on the Fraction of Stars With Planets as Small as 0.3 R_J
We present the results of a deep (15 ~< r ~< 23), 20 night survey for
transiting planets in the intermediate age open cluster M37 (NGC 2099) using
the Megacam wide-field mosaic CCD camera on the 6.5m MMT. We do not detect any
transiting planets among the ~1450 observed cluster members. We do, however,
identify a ~ 1 R_J candidate planet transiting a ~ 0.8 Msun Galactic field star
with a period of 0.77 days. The source is faint (V = 19.85 mag) and has an
expected velocity semi-amplitude of K ~ 220 m/s (M/M_J). We conduct Monte Carlo
transit injection and recovery simulations to calculate the 95% confidence
upper limit on the fraction of cluster members and field stars with planets as
a function of planetary radius and orbital period. Assuming a uniform
logarithmic distribution in orbital period, we find that < 1.1%, < 2.7% and <
8.3% of cluster members have 1.0 R_J planets within Extremely Hot Jupiter (EHJ,
0.4 < T < 1.0 day), Very Hot Jupiter (VHJ, 1.0 < T < 3.0 days) and Hot Jupiter
(HJ, 3.0 < T < 5.0 days) period ranges respectively. For 0.5 R_J planets the
limits are < 3.2%, and < 21% for EHJ and VHJ period ranges, while for 0.35 R_J
planets we can only place an upper limit of < 25% on the EHJ period range. For
a sample of 7814 Galactic field stars, consisting primarily of FGKM dwarfs, we
place 95% upper limits of < 0.3%, < 0.8% and < 2.7% on the fraction of stars
with 1.0 R_J EHJ, VHJ and HJ assuming the candidate planet is not genuine. If
the candidate is genuine, the frequency of ~ 1.0 R_J planets in the EHJ period
range is 0.002% < f_EHJ < 0.5% with 95% confidence. We place limits of < 1.4%,
< 8.8% and < 47% for 0.5 R_J planets, and a limit of < 16% on 0.3 R_J planets
in the EHJ period range. This is the first transit survey to place limits on
the fraction of stars with planets as small as Neptune.Comment: 61 pages, 19 figures, 5 tables, replaced with the version accepted
for publication in Ap
A 22-year Southern Sky Survey for Transient and Variable Radio Sources using the Molonglo Observatory Synthesis Telescope
We describe a 22-year survey for variable and transient radio sources,
performed with archival images taken with the Molonglo Observatory Synthesis
Telescope (MOST). This survey covers 2775 \unit{deg^2} of the sky south of
at an observing frequency of 843 MHz, an angular
resolution of 45 \times 45 \csc | \delta| \unit{arcsec^2} and a sensitivity
of 5 \sigma \geq 14 \unit{mJy beam^{-1}}. We describe a technique to
compensate for image gain error, along with statistical techniques to check and
classify variability in a population of light curves, with applicability to any
image-based radio variability survey. Among radio light curves for almost 30000
sources, we present 53 highly variable sources and 15 transient sources. Only 3
of the transient sources, and none of the variable sources have been previously
identified as transient or variable. Many of our variable sources are suspected
scintillating Active Galactic Nuclei. We have identified three variable sources
and one transient source that are likely to be associated with star forming
galaxies at , but whose implied luminosity is higher than the
most luminous known radio supernova (SN1979C) by an order of magnitude. We also
find a class of variable and transient source with no optical counterparts.Comment: Accepted for publication in MNRAS. 34 pages, 30 figures, 7 table
Some empirical estimates of the H2 formation rate in photon-dominated regions
We combine recent ISO observations of the vibrational ground state lines of
H2 towards Photon-Dominated Regions (PDRs) with observations of vibrationally
excited states made with ground-based telescopes in order to constrain the
formation rate of H2 on grain surfaces under the physical conditions in the
layers responsible for H2 emission. We use steady state PDR models in order to
examine the sensitivity of different H2 line ratios to the H2 formation rate
Rf. We show that the ratio of the 0-0 S(3) to the 1-0 S(1) line increases with
Rf but that one requires independent estimates of the radiation field incident
upon the PDR and the density in order to infer Rf from the H2 line data. We
confirm the earlier result of Habart et al. (2003) that the H2 formation rate
in regions of moderate excitation such as Oph W, S140 and IC 63 is a factor of
5 times larger than the standard rate inferred from UV observations of diffuse
clouds. On the other hand, towards regions of higher radiation field such as
the Orion Bar and NGC 2023, we derive H2 formation rates consistent with the
standard value. We find also a correlation between the H2 1-0 S(1) line and PAH
emission suggesting that Rf scales with the PAH abundance. With the aim of
explaining these results, we consider some empirical models of the H2 formation
process. Here we consider both formation on big (a~0.1 microns) and small (a~10
Angstroms) grains by either direct recombination from the gas phase or
recombination of physisorbed H atoms with atoms in a chemisorbed site. We
conclude that indirect chemisorption is most promising in PDRs. Moreover small
grains which dominate the total grain surface and spend most of their time at
relatively low temperatures may be the most promising surface for forming H2 in
PDRs.Comment: A&A in press, 16 pages, 5 figure
Searching for transits in the Wide Field Camera Transit Survey with difference-imaging light curves
The Wide Field Camera Transit Survey is a pioneer program aiming at for searching extra-solar planets in the near-infrared. The images from the survey are processed by a data reduction pipeline, which uses aperture photometry to construct the light curves. We produce an alternative set of light curves using the difference-imaging method for the most complete field in the survey and carry out a quantitative comparison between the photometric precision achieved with both methods. The results show that differencephotometry light curves present an important improvement for stars with J > 16. We report an implementation on the box-fitting transit detection algorithm, which performs a trapezoid-fit to the folded light curve, providing more accurate results than the boxfitting model. We describe and optimize a set of selection criteria to search for transit candidates, including the V-shape parameter calculated by our detection algorithm. The optimized selection criteria are applied to the aperture photometry and difference-imaging light curves, resulting in the automatic detection of the best 200 transit candidates from a sample of ~475 000 sources. We carry out a detailed analysis in the 18 best detections and classify them as transiting planet and eclipsing binary candidates. We present one planet candidate orbiting a late G-type star. No planet candidate around M-stars has been found, confirming the null detection hypothesis and upper limits on the occurrence rate of short-period giant planets around M-dwarfs presented in a prior study. We extend the search for transiting planets to stars with J ≤ 18, which enables us to set a stricter upper limit of 1.1%. Furthermore, we present the detection of five faint extremely-short period eclipsing binaries and three M-dwarf/M-dwarf binary candidates. The detections demonstrate the benefits of using the difference-imaging light curves, especially when going to fainter magnitudes.Peer reviewe
Supermassive Black Hole Binaries: The Search Continues
Gravitationally bound supermassive black hole binaries (SBHBs) are thought to
be a natural product of galactic mergers and growth of the large scale
structure in the universe. They however remain observationally elusive, thus
raising a question about characteristic observational signatures associated
with these systems. In this conference proceeding I discuss current theoretical
understanding and latest advances and prospects in observational searches for
SBHBs.Comment: 17 pages, 4 figures. To appear in the Proceedings of 2014 Sant Cugat
Forum on Astrophysics. Astrophysics and Space Science Proceedings, ed.
C.Sopuerta (Berlin: Springer-Verlag
Spinor condensates and light scattering from Bose-Einstein condensates
These notes discuss two aspects of the physics of atomic Bose-Einstein
condensates: optical properties and spinor condensates. The first topic
includes light scattering experiments which probe the excitations of a
condensate in both the free-particle and phonon regime. At higher light
intensity, a new form of superradiance and phase-coherent matter wave
amplification were observed. We also discuss properties of spinor condensates
and describe studies of ground--state spin domain structures and dynamical
studies which revealed metastable excited states and quantum tunneling.Comment: 58 pages, 33 figures, to appear in Proceedings of Les Houches 1999
Summer School, Session LXXI
Planetary Candidates Observed by Kepler, III: Analysis of the First 16 Months of Data
New transiting planet candidates are identified in sixteen months (May 2009 -
September 2010) of data from the Kepler spacecraft. Nearly five thousand
periodic transit-like signals are vetted against astrophysical and instrumental
false positives yielding 1,091 viable new planet candidates, bringing the total
count up to over 2,300. Improved vetting metrics are employed, contributing to
higher catalog reliability. Most notable is the noise-weighted robust averaging
of multi-quarter photo-center offsets derived from difference image analysis
which identifies likely background eclipsing binaries. Twenty-two months of
photometry are used for the purpose of characterizing each of the new
candidates. Ephemerides (transit epoch, T_0, and orbital period, P) are
tabulated as well as the products of light curve modeling: reduced radius
(Rp/R*), reduced semi-major axis (d/R*), and impact parameter (b). The largest
fractional increases are seen for the smallest planet candidates (197% for
candidates smaller than 2Re compared to 52% for candidates larger than 2Re) and
those at longer orbital periods (123% for candidates outside of 50-day orbits
versus 85% for candidates inside of 50-day orbits). The gains are larger than
expected from increasing the observing window from thirteen months (Quarter 1--
Quarter 5) to sixteen months (Quarter 1 -- Quarter 6). This demonstrates the
benefit of continued development of pipeline analysis software. The fraction of
all host stars with multiple candidates has grown from 17% to 20%, and the
paucity of short-period giant planets in multiple systems is still evident. The
progression toward smaller planets at longer orbital periods with each new
catalog release suggests that Earth-size planets in the Habitable Zone are
forthcoming if, indeed, such planets are abundant.Comment: Submitted to ApJS. Machine-readable tables are available at
http://kepler.nasa.gov, http://archive.stsci.edu/kepler/results.html, and the
NASA Exoplanet Archiv
Masses, radii, and orbits of small Kepler planets : The transition from gaseous to rocky planets
We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm-3, suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than 2 R ⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H2O).Peer reviewedFinal Accepted Versio
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