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Post Info TOPIC: Solar neighbourhood
Blobrana


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RE: Solar neighbourhood
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Title: An overabundance of oxygen in planetary nebulae of the solar neighbourhood
Authors: Mónica Rodríguez, Gloria Delgado-Inglada

We study the oxygen abundance in five H II regions and seven planetary nebulae (PNe) located within 2 kpc from the Sun that have available spectra of high quality. Our analysis uses a similar procedure and the same atomic data to derive abundances in all the objects. The results calculated with collisionally excited lines for the H II regions indicate that the local interstellar medium is very homogeneous, with 12+log(O/H)=8.45-8.54. As for the PNe, six out of seven show significantly higher abundances: 12+log(O/H)=8.65-8.80. This overabundance of oxygen in PNe also holds when we consider the abundances implied by recombination lines.

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Blobrana


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Title: The Solar Neighbourhood. XXII. Parallax Results from the CTIOPI 0.9m Program: Trigonometric Parallaxes of 64 Nearby Systems with >= 10 yr^-1 (SLOWMO sample)
Authors: Adric R. Riedel, John P. Subasavage, Charlie T. Finch, Wei Chun Jao, Todd J. Henry, Jennifer G. Winters, Misty A. Brown, Philip A. Ianna, Edgardo Costa, Rene A. Mendez

We present trigonometric parallaxes of 64 stellar systems with proper motions between 0\farcs5 yr^{-1} and 1\farcs0 yr^{-1} from the ongoing RECONS (Research Consortium On Nearby Stars) parallax program at CTIO (the Cerro Tololo Interamerican Observatory). All of the systems are south of DEC = +30, and 58 had no previous trigonometric parallaxes. In addition to parallaxes for the systems, we present proper motions, Johnson-Kron-Cousins VRI photometry, variability measurements, and spectral types. Nine of the systems are multiple; we present results for their components, three of which are new astrometric detections. Of the 64 systems, 56 are within 25 parsecs of the Sun and 52 of those are in the southern hemisphere, comprising 5.7% of the total number of known southern 25 parsec systems.

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Blobrana


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Title: Searching for Stars Closely Encountering with the Solar System
Authors: Vadim V. Bobylev

Based on a new version of the Hipparcos catalogue and currently available radial velocity data, we have searched for stars that either have encountered or will encounter the solar neighbourhood within less than 3 pc in the time interval from -2 Myr to +2 Myr. Nine new candidates within 30 pc of the Sun have been found. To construct the stellar orbits relative to the solar orbit, we have used the epicyclic approximation. We show that, given the errors in the observational data, the probability that the well-known star HIP 89 825 (GL 710) encountering with the Sun most closely falls into the Oort cloud is 0.86 in the time interval 1.45±0.06 Myr. This star also has a nonzero probability, 0.0001, of falling into the region d<1000 AU, where its influence on Kuiper Belt objects becomes possible.

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Blobrana


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Posts: 131433
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Young Low-mass Stars
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Title: Identifying the Young Low-mass Stars within 25 pc. I. Spectroscopic Observations
Authors: Evgenya Shkolnik (DTM/CIW), Michael C. Liu (IfA/UH), I. Neill Reid (STScI)

We have completed a high-resolution (R=60,000) optical spectroscopic survey of 185 nearby M dwarfs identified using ROSAT data to select active, young objects with fractional X-ray luminosities comparable to or greater than Pleiades members. Our targets are drawn from the NStars 20-pc census and the Moving-M sample with distances determined from parallaxes or spectrophotometric relations. Nearly half of the resulting M dwarfs are not present in the Gliese catalogue and have no previously published spectral types. We identified 30 spectroscopic binaries (SBs) from the sample, which have strong X-ray emission due to tidal spin-up rather than youth. This is equivalent to a 16% spectroscopic binary fraction, with at most a handful of undiscovered SBs. We estimate upper limits on the age of the remaining M dwarfs using spectroscopic youth indicators such as surface gravity-sensitive indices (CaH and K I). We find that for a sample of field stars with no metallicity measurements, a single CaH gravity index may not be sufficient, as higher metallicities mimic lower gravity. This is demonstrated in a sub-sample of metal-rich RV standards, which appear to have low surface gravity as measured by the CaH index, yet show no other evidence of youth. We also use additional youth diagnostics such as lithium absorption and strong H-alpha emission to set more stringent age limits. Eleven M dwarfs with no H-alpha emission or absorption are likely old (>400 Myr) and were caught during an X-ray flare. We estimate that our final sample of the 144 youngest and nearest low-mass objects in the field is less than 300 Myr old, with 30% of them being younger than 150 Myr and 4 very young (<10 Myr), representing a generally untapped and well-characterised resource of M dwarfs for intensive planet and disk searches.

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Blobrana


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Posts: 131433
Date:
Solar Neighbourhood
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Title: The Solar Neighbourhood. XXI. Parallax Results from the CTIOPI 0.9m Program: 20 New Members of the 25 Parsec White Dwarf Sample
Authors: John P. Subasavage (1), Wei-Chun Jao (1), Todd J. Henry (1), P. Bergeron (2), P. Dufour (3), Philip A. Ianna (4), Edgardo Costa (5), Rene A. Mendez (5), ((1) Georgia State University, (2) University of Montreal, (3) University of Arizona, (4) University of Virginia, (5) University of Chile)

We present accurate trigonometric parallaxes for 20 new members of the 25 pc white dwarf sample as part of the DENSE project. Previously, there were a total of 112 white dwarf systems with trigonometric parallaxes placing them within 25 pc and of these, 99 have trigonometric parallaxes known to better than 10%. Thus, the 20 new members presented in this work represent a 20% increase in the number of white dwarfs accurately known to be within 25 pc. In addition, we present updated parallaxes for seven known white dwarfs within 10 pc that have been observed as part of the ASPENS initiative (Astrometric Search for Planets Encircling Nearby Stars) to monitor nearby southern red and white dwarfs for astrometric perturbations from unseen companions. Including a few white dwarf companions and white dwarfs beyond 25 pc, we present a total of 33 trigonometric parallaxes. We perform atmospheric modelling for white dwarfs to determine physical parameters (i.e., effective temperature, log g, mass, and white dwarf age). Finally, a new ZZ Ceti pulsating white dwarf was identified and revised constraints are placed on two mixed H/He atmosphere cool white dwarfs that display continuum absorption in the near-infrared.

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Discovery and Evalution of Nearby Stellar Embers


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Blobrana


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Title: New Neighbours: Parallaxes of 18 nearby stars selected from the LSPM-north catalogue
Authors: Sebastien Lepine, John R. Thorstensen, Michael M. Shara, R. Michael Rich

We present astrometric parallaxes for 18 suspected nearby stars selected from the LSPM-north proper motion catalogue. Sixteen objects are confirmed to be main sequence M dwarfs within 16 parsecs of the Sun, including three stars (LSPM J0011+5908, LSPM J0330+5413, LSPM J0510+2714) which lie just within the 10 parsec horizon. Two other targets (LSPM J1817+1328, LSPM J2325+1403) are confirmed to be nearby white dwarfs at distances of 14 and 22 parsecs, respectively. One of our targets, the common proper motion pair LSPM J0405+7116E + LSPM J0405+7116W, is revealed to be a triple system, with the western component resolved into a pair of 16th magnitude stars (LSPM J0405+7116W-A and LSPM J0405+7116W-B) with a 0.7" ±0.1" angular separation. We find two stars (LSPM J1314+1320 and LSPM J1757+7042) to be significantly over luminous for their colours, and suggest that these may be unresolved doubles/multiples.

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Blobrana


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Title: From 1000 AU to 1000 pc: high proper-motion stars in the solar neighbourhood, radio sources in the sigma Orionis cluster, and new X-ray stars surrounding Alnilam
Authors: Jose A. Caballero
(Version v2)

The Virtual Observatory is useful. I summarise some of my works where I extensively use the Aladin sky atlas. Topics cover from the search and common proper motion confirmation of very low-mass stars and brown dwarfs in wide (rho > 1000 AU) binaries and multiple systems, to the identification and characterisation of stellar and substellar populations in young open clusters and OB associations at heliocentric distances of up to 1000 pc. I present three practical examples of what one can do with Aladin in one morning: a fruitful proper-motion search of objects with available ugrizJHKs photometry, an analysis of the 21 cm radio sources towards the young sigma Orionis cluster, and a novel study of X-ray young stars surrounding Alnilam in the Orion Belt.

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Blobrana


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Title: Our Nearest 15 Million Neighbours: The Field Low-Mass Stellar Luminosity and Mass Functions
Authors: John J. Bochanski, Suzanne L. Hawley, I. Neill Reid, Kevin R. Covey, Andrew A. West, David A. Golimowski, Zeljko Ivezic

We report on a new measurement of the luminosity function (LF) and mass function (MF) of field low-mass dwarfs using Sloan Digital Sky Survey (SDSS) photometry. The final catalogue is composed of ~15 million low-mass stars (0.1 Msun < M < 0.8 Msun), spread over 8,400 square degrees. Distances to the stars are estimated using new photometric parallax relations, constructed from ugriz photometry of nearby low-mass stars with trigonometric parallaxes. The LF is measured with a novel technique, which simultaneously measures Galactic structure and the stellar LF. The resulting LF is compared to previous studies and converted to a MF. The MF is well-described by a log-normal distribution, with Mo = 0.27 Msun.

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Blobrana


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Title: A Distance-Limited Imaging Survey of Sub-Stellar Companions to Solar Neighbourhood Stars
Authors: Joseph C. Carson, Kyle D. Hiner, Gregorio G. Villar III, Michael G. Blaschak, Alexander L. Rudolph, Karl R. Stapelfeldt

We report techniques and results of a Palomar 200-inch (5 m) adaptive optics imaging survey of sub-stellar companions to solar-type stars. The survey consists of Ks coronagraphic observations of 21 FGK dwarfs out to 20 pc (median distance about 17 pc). At 1-arcsec separation (17 projected AU) from a typical target system, the survey achieves median sensitivities 7 mag fainter than the parent star. In terms of companion mass, that corresponds to sensitivities of 50MJ (1 Gyr), 70MJ (solar age), and 75MJ (10 Gyr), using the evolutionary models of Baraffe and colleagues. Using common proper motion to distinguish companions from field stars, we find that no system shows positive evidence of a previously unknown substellar companion (searchable separation about 20-250 projected AU at the median target distance).

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Blobrana


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Title: Searching for the metal-weak thick disc in the solar neighbourhood
Authors: Bacham E. Reddy, David L. Lambert

An abundance analysis is presented of 60 metal-poor stars drawn from catalogues of nearby stars provided by Ariyanto et al. (2005) and Schuster et al. (2006). In an attempt to isolate a sample of metal-weak thick disc stars, we applied the kinematic criteria V_{
m rot} \geq 100 km s^{-1}, |U_{LSR}| \leq 140 km s^{-1}, and |W_{LSR}| \leq 100 km s^{-1}. Fourteen stars satisfying these criteria and having [Fe/H] \leq -1.0 are included in the sample of 60 stars. Eight of the 14 have [Fe/H] \geq -1.3 and may be simply thick disc stars of slightly lower than average [Fe/H]. The other six have [Fe/H] from -1.3 to -2.3 and are either metal-weak thick disc stars or halo stars with kinematics mimicking those of the thick disc. The sample of 60 stars is completed by eight thick disc stars, 20 stars of a hybrid nature (halo or thick disc stars), and 18 stars with kinematics distinctive of the halo.

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