555 research outputs found
The Solar Neighborhood XVII: Parallax Results from the CTIOPI 0.9m Program -- Twenty New Members of the RECONS 10 Parsec Sample
Astrometric measurements for 25 red dwarf systems are presented, including
the first definitive trigonometric parallaxes for 20 systems within 10 pc of
the Sun, the horizon of the RECONS sample. The three nearest systems that had
no previous trigonometric parallaxes (other than perhaps rough preliminary
efforts) are SO 0253+1652 (3.84 +/- 0.04 pc, the 23rd nearest system), SCR
1845-6357 AB (3.85 +/- 0.02 pc, 24th), and LHS 1723 (5.32 +/- 0.04 pc, 56th).
In total, seven of the systems reported here rank among the nearest 100 stellar
systems. Supporting photometric and spectroscopic observations have been made
to provide full characterization of the systems, including complete VRIJHK
photometry and spectral types. A study of the variability of 27 targets reveals
six obvious variable stars, including GJ 1207, for which we observed a flare
event in the V band that caused it to brighten by 1.7 mag.
Improved parallaxes for GJ 54 AB and GJ 1061, both important members of the
10 pc sample, are also reported. Definitive parallaxes for GJ 1001 A, GJ 633,
and GJ 2130 ABC, all of which have been reported to be within 10 pc, indicate
that they are beyond 10 pc. From the analysis of systems with (previously) high
trigonometric parallax errors, we conclude that parallaxes with errors in
excess of 10 mas are insufficiently reliable for inclusion in the RECONS
sample. The cumulative total of new additions to the 10 pc sample since 2000 is
now 34 systems -- 28 by the RECONS team and six by other groups. This total
represents a net increase of 16% in the number of stellar systems reliably
known to be nearer than 10 pc.Comment: 33 pages, including 3 figures and 3 table
Target selection for the SUNS and DEBRIS surveys for debris discs in the solar neighbourhood
Debris discs - analogous to the Asteroid and Kuiper-Edgeworth belts in the
Solar system - have so far mostly been identified and studied in thermal
emission shortward of 100 um. The Herschel space observatory and the SCUBA-2
camera on the James Clerk Maxwell Telescope will allow efficient photometric
surveying at 70 to 850 um, which allow for the detection of cooler discs not
yet discovered, and the measurement of disc masses and temperatures when
combined with shorter wavelength photometry. The SCUBA-2 Unbiased Nearby Stars
(SUNS) survey and the DEBRIS Herschel Open Time Key Project are complimentary
legacy surveys observing samples of ~500 nearby stellar systems. To maximise
the legacy value of these surveys, great care has gone into the target
selection process. This paper describes the target selection process and
presents the target lists of these two surveys.Comment: 67 pages with full tables, 7 figures, accepted to MNRA
The Multiplicity of Massive Stars: A High Angular Resolution Survey with the HST Fine Guidance Sensor
We present the results of an all-sky survey made with the Fine Guidance
Sensor on Hubble Space Telescope to search for angularly resolved binary
systems among the massive stars. The sample of 224 stars is comprised mainly of
Galactic O- and B-type stars and Luminous Blue Variables, plus a few luminous
stars in the Large Magellanic Cloud. The FGS TRANS mode observations are
sensitive to detection of companions with an angular separation between 0."01
and 1."0 and brighter than . The FGS observations resolved 52
binary and 6 triple star systems and detected partially resolved binaries in 7
additional targets (43 of these are new detections). These numbers yield a
companion detection frequency of 29% for the FGS survey. We also gathered
literature results on the numbers of close spectroscopic binaries and wider
astrometric binaries among the sample, and we present estimates of the
frequency of multiple systems and the companion frequency for subsets of stars
residing in clusters and associations, field stars, and runaway stars. These
results confirm the high multiplicity fraction, especially among massive stars
in clusters and associations. We show that the period distribution is
approximately flat in increments of log P. We identify a number of systems of
potential interest for long term orbital determinations, and we note the
importance of some of these companions for the interpretation of the radial
velocities and light curves of close binaries that have third companions.Comment: 37 pages, 4 figures, 5 tables; AJ, in press; Full version with
extended tables and large figure set can be found:
http://www.astro.umontreal.ca/~emily/fgs.pd
Trumpeting M Dwarfs with CONCH-SHELL: a Catalog of Nearby Cool Host-Stars for Habitable ExopLanets and Life
We present an all-sky catalog of 2970 nearby ( pc), bright
() M- or late K-type dwarf stars, 86% of which have been confirmed by
spectroscopy. This catalog will be useful for searches for Earth-size and
possibly Earth-like planets by future space-based transit missions and
ground-based infrared Doppler radial velocity surveys. Stars were selected from
the SUPERBLINK proper motion catalog according to absolute magnitudes, spectra,
or a combination of reduced proper motions and photometric colors. From our
spectra we determined gravity-sensitive indices, and identified and removed
0.2% of these as interloping hotter or evolved stars. Thirteen percent of the
stars exhibit H-alpha emission, an indication of stellar magnetic activity and
possible youth. The mean metallicity is [Fe/H] = -0.07 with a standard
deviation of 0.22 dex, similar to nearby solar-type stars. We determined
stellar effective temperatures by least-squares fitting of spectra to model
predictions calibrated by fits to stars with established bolometric
temperatures, and estimated radii, luminosities, and masses using empirical
relations. Six percent of stars with images from integral field spectra are
resolved doubles. We inferred the planet population around M dwarfs using
data and applied this to our catalog to predict detections by future
exoplanet surveys.Comment: Accepted to MNRAS 22 figures, 3 tables, 2 electronic tables.
Electronic tables are available as links on this pag
Three red suns in the sky: A transiting, terrestrial planet in a triple M-dwarf system at 6.9 pc
We present the discovery from Transiting Exoplanet Survey Satellite (TESS) data of LTT 1445Ab. At a distance of 6.9 pc, it is the second nearest transiting exoplanet system found to date, and the closest one known for which the primary is an M dwarf. The host stellar system consists of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in one TESS pixel. We use MEarth data and results from the Science Processing Operations Center data validation report to determine that the planet transits the primary star in the system. The planet has a radius of , an orbital period of days, and an equilibrium temperature of K. With radial velocities from the High Accuracy Radial Velocity Planet Searcher, we place a 3σ upper mass limit of 8.4 on the planet. LTT 1445Ab provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world. We also present a detailed characterization of the host stellar system. We use high-resolution spectroscopy and imaging to rule out the presence of any other close stellar or brown dwarf companions. Nineteen years of photometric monitoring of A and BC indicate a moderate amount of variability, in agreement with that observed in the TESS light-curve data. We derive a preliminary astrometric orbit for the BC pair that reveals an edge-on and eccentric configuration. The presence of a transiting planet in this system hints that the entire system may be co-planar, implying that the system may have formed from the early fragmentation of an individual protostellar core.Accepted manuscrip
RARRES3 expression positively correlated to tumour differentiation in tissues of colorectal adenocarcinoma
Shape model and spin-state analysis of PHA contact binary (85990) 1999 JV6 from combined radar and optical observations
Context. The potentially hazardous asteroid (85990)1999 JV6 has been a target of previously published thermal-infrared observations and optical photometry. It has been identified as a promising candidate for possible Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect detection.
Aims. The YORP effect is a small thermal-radiation torque considered to be a key factor in spin-state evolution of small Solar System bodies. In order to detect YORP on 1999 JV6 we developed a detailed shape model and analysed the spin-state using both optical and radar observations.
Methods. For 1999 JV6, we collected optical photometry between 2007 and 2016. Additionally, we obtained radar echo-power spectra and imaging observations with Arecibo and Goldstone planetary radar facilities in 2015, 2016, and 2017. We combined our data with published optical photometry to develop a robust physical model.
Results. We determine that the rotation pole resides at negative latitudes in an area with a 5◦ radius close to the south ecliptic pole. The refined sidereal rotation period is 6.536787±0.000007 h. The radar images are best reproduced with a bilobed shape model. Both lobes of 1999 JV6 can be represented as oblate ellipsoids with a smaller, more spherical component resting at the end of a larger, more elongated component. While contact binaries appear to be abundant in the near-Earth population, there are only a few published shape models for asteroids in this particular configuration. By combining the radar-derived shape model with optical light curves we determine a constant-period solution that fits all available data well. Using light-curve data alone we determine an upper limit for YORP of 8.5×10−8 rad day−2.
Conclusions. The bifurcated shape of 1999 JV6 might be a result of two ellipsoidal components gently merging with each other, or a deformation of a rubble pile with a weak-tensile-strength core due to spin-up. The physical model of 1999 JV6 presented here will enable future studies of contact binary asteroid formation and evolution
A rocky planet transiting a nearby low-mass star
M-dwarf stars -- hydrogen-burning stars that are smaller than 60 per cent of
the size of the Sun -- are the most common class of star in our Galaxy and
outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M
dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf
planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per
star. The nearest such planets known to transit their star are 39 parsecs away,
too distant for detailed follow-up observations to measure the planetary masses
or to study their atmospheres. Here we report observations of GJ 1132b, a
planet with a size of 1.2 Earth radii that is transiting a small star 12
parsecs away. Our Doppler mass measurement of GJ 1132b yields a density
consistent with an Earth-like bulk composition, similar to the compositions of
the six known exoplanets with masses less than six times that of the Earth and
precisely measured densities. Receiving 19 times more stellar radiation than
the Earth, the planet is too hot to be habitable but is cool enough to support
a substantial atmosphere, one that has probably been considerably depleted of
hydrogen. Because the host star is nearby and only 21 per cent the radius of
the Sun, existing and upcoming telescopes will be able to observe the
composition and dynamics of the planetary atmosphere.Comment: Published in Nature on 12 November 2015, available at
http://dx.doi.org/10.1038/nature15762. This is the authors' version of the
manuscrip
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