Oph 1622-2405: Not a Planetary-Mass Binary

We present an analysis of the mass and age of the young low-mass binary Oph 1622-2405. Using resolved optical spectroscopy of the binary, we measure spectral types of M7.25+/-0.25 and M8.75+/-0.25 for the A and B components, respectively. We show that our spectra are inconsistent with the spectral types of M9 and M9.5-L0 from Jayawardhana & Ivanov and M9+/-0.5 and M9.5+/-0.5 from Close and coworkers. Based on our spectral types and the theoretical evolutionary models of Chabrier and Baraffe, we estimate masses of 0.055 and 0.019 Msun for Oph 1622-2405A and B, which are significantly higher than the values of 0.013 and 0.007 Msun derived by Jayawardhana & Ivanov and above the range of masses observed for extrasolar planets (M<=0.015 Msun). Planet-like mass estimates are further contradicted by our demonstration that Oph 1622-2405A is only slightly later (by 0.5 subclass) than the composite of the young eclipsing binary brown dwarf 2M 0535-0546, whose components have dynamical masses of 0.034 and 0.054 Msun. To constrain the age of Oph 1622-2405, we compare the strengths of gravity-sensitive absorption lines in optical and near-infrared spectra of the primary to lines in field dwarfs (>1 Gyr) and members of Taurus (~1 Myr) and Upper Scorpius (~5 Myr). The line strengths for Oph 1622-2405A are inconsistent with membership in Ophiuchus (<1 Myr) and instead indicate an age similar to that of Upper Sco, which is agreement with a similar analysis performed by Close and coworkers. We conclude that Oph 1622-2405 is part of an older population in Sco-Cen, perhaps Upper Sco itself.Comment: The Astrophysical Journal, in pres

Exploring Halo Substructure with Giant Stars III: First Results from the Grid Giant Star Survey and Discovery of a Possible Nearby Sagittarius Tidal Structure in Virgo

We describe first results of a spectroscopic probe of selected fields from the Grid Giant Star Survey. Multifiber spectroscopy of several hundred stars in a strip of eleven fields along delta approximately -17^{circ}, in the range 12 <~ alpha <~ 17 hours, reveals a group of 8 giants that have kinematical characteristics differing from the main field population, but that as a group maintain coherent, smoothly varying distances and radial velocities with position across the fields. Moreover, these stars have roughly the same abundance, according to their MgH+Mgb absorption line strengths. Photometric parallaxes place these stars in a semi-loop structure, arcing in a contiguous distribution between 5.7 and 7.9 kpc from the Galactic center. The spatial, kinematical, and abundance coherence of these stars suggests that they are part of a diffuse stream of tidal debris, and one roughly consistent with a wrapped, leading tidal arm of the Sagittarius dwarf spheroidal galaxy.Comment: 8 pages including 4 figures. Accepted for publication in ApJ

A Constraint on brown dwarf formation via ejection: radial variation of the stellar and substellar mass function of the young open cluster IC2391

Using the Wide Field Imager (WFI) at the ESO 2.2m telescope at La Silla and the CPAPIR camera at the CTIO 1.5m telescope at Cerro Tololo, we have performed an extensive, multiband photometric survey of the open cluster IC2391 (D~146pc, age~50Myr, solar metallicity). Here we present the results from our photometric survey and from a spectroscopic follow-up of the central part of the survey.Comment: 4 pages, 3 figures, to appear in the proceedings of the Cool Stars 15 conferenc

Searching for Young M Dwarfs with GALEX

The census of young moving groups in the solar neighborhood is significantly incomplete in the low-mass regime. We have developed a new selection process to find these missing members based on the GALEX All-Sky Imaging Survey. For stars with spectral types >K5 and younger than 300~Myr, we show that near-UV and far-UV emission is greatly enhanced above the quiescent photosphere, analogous to the enhanced X-ray emission of young low-mass stars seen by ROSAT but detectable to much larger distances with GALEX. By combining GALEX data with optical (HST Guide Star Catalog) and near-IR (2MASS) photometry, we identified an initial sample of 34 young M dwarf candidates in a 1000 sq.~deg.~region around the 10-Myr TW Hydra Association (TWA). Low-resolution spectroscopy of 30 of these found 16 which had H_alpha in emission, which were then followed-up at high resolution to search for spectroscopic evidence of youth and to measure radial velocities. Four objects have low surface gravities, photometric distances and space motions consistent with TWA, but the non-detection of Li indicates they may be too old to belong to this moving group. One object (M3.5, 93 pc) appears to be the first known accreting low-mass member of the 15~Myr Lower Centaurus Crux OB association. Two objects exhibit all the characteristics of the known TWA members, and thus we designate them as TWA 31 (M4.2, 110 pc) and TWA 32 (M6.3, 53 pc). TWA 31 shows extremely broad (447 km/s) H_alpha emission, making it the sixth member of TWA found to have ongoing accretion. TWA 32 is resolved into a 0.6" binary in Keck laser guide star adaptive optics imaging. Our search should be sensitive down to spectral types of at least M4-M5 in TWA and thus the small numbers of new member is puzzling. This may indicate TWA has an atypical mass function or that the presence of Li may be too restrictive a criteria for selecting young low-mass stars.Comment: Accepted to Ap

Fatal septicemia in a patient with cerebral lymphoma and an Amplatzer septal occluder: a case report

<p>Abstract</p> <p>Introduction</p> <p>The Amplatzer septal occluder is frequently used for percutaneous closure of an atrial septal defect. Complications include thrombosis and embolism, dislocation, cardiac perforation, and, rarely, infection. We report the case of a patient who had survived an occluder-related thromboembolism two years previously.</p> <p>Case presentation</p> <p>A 72-year-old Caucasian woman had received a septal occluder because of an atrial septal defect seven years ago. Two years ago, she underwent chemotherapy of a non-Hodgkin lymphoma, developed atrial fibrillation, and experienced a left-sided occluder thrombosis with stroke and peripheral embolism. Now, she presented with cerebral lymphoma, received glucocorticoids, and subsequently developed skin lesions. Swabs from the lesions and blood cultures were positive for methicillin-resistant <it>Staphylococcus aureus </it>and <it>Pseudomonas aeruginosa</it>. Endocarditis, however, was considered only two months later and echocardiography suggested aortic valve endocarditis. Despite antibiotic therapy, she died three days later because of septicemia, and no post-mortem investigation was carried out. It remains uncertain whether the septal occluder was endothelialized or infected and whether explantation might have changed the outcome.</p> <p>Conclusions</p> <p>If infections occur in patients with a septal occluder, endocarditis should be considered and echocardiography should be performed early. To prevent a fatal outcome, explantation of the septal occluder should be considered, especially in patients with problems that suggest delayed endothelialization. Post-mortem investigations, including bacteriologic studies, should be carried out in patients with a septal occluder in order to assess the focal and global long-term effects of these devices.</p

The Greater Taurus–Auriga Ecosystem. I. There is a Distributed Older Population

The census of Taurus–Auriga has been assembled over seven decades and inherited the biases and incompleteness of the input studies. The unusual shape of its inferred initial mass function (IMF) and the existence of isolated disk-bearing stars suggest that additional (likely disk-free) members remain to be discovered. We therefore have begun a global reassessment of the census of Taurus–Auriga that exploits new data and better definitions of youth and kinematic membership. As a first step, we reconsider the membership of all disk-free candidate members from the literature with spectral type ≥F0, 3^h50^m < α < 5^h40^m, and 14° < δ < 34°. We combine data from the literature with Keck/HIRES and UH88/SNIFS spectra to test the membership of these candidates using the positions in the Hertzsprung-Russel diagram, proper motions, radial velocities, Hα, lithium, and surface gravity. We find 218 confirmed or likely Taurus members, 160 confirmed or likely interlopers, and only 18 that lack sufficient evidence to draw firm conclusions. A significant fraction of these stars (81/218 = 37%) are not included in the most recent canonical member lists. There are few additional members to the immediate vicinity of the molecular clouds, preserving the IMFs that have been deemed anomalous in past work. Many of the likely Taurus members are instead distributed broadly across the search area. When combined with the known disk hosts, our updated census reveals two regimes: a high-density population with a high disk fraction (indicative of youth) that broadly traces the molecular clouds, and a low-density population with low disk fraction (hence likely older) that most likely represents previous generations of star formation

The Mass Function of Newly Formed Stars (Review)

The topic of the stellar "original mass function" has a nearly 50 year history,dating to the publication in 1955 of Salpeter's seminal paper. In this review I discuss the many more recent results that have emerged on the initial mass function (IMF), as it is now called, from studies over the last decade of resolved populations in star forming regions and young open clusters.Comment: 9 pages, 1 figure; to appear in "The Dense Instellar Medium in Galaxies -- 4'th Cologne-Bonn-Zermatt-Symposium" editted by S. Pfalzner, C. Kramer, C. Straubmeier and A. Heithausen, Springer-Verlag (2004

Thirty New Low-Mass Spectroscopic Binaries

As part of our search for young M dwarfs within 25 pc, we acquired high-resolution spectra of 185 low-mass stars compiled by the NStars project that have strong X-ray emission. By cross-correlating these spectra with radial velocity standard stars, we are sensitive to finding multi-lined spectroscopic binaries. We find a low-mass spectroscopic binary fraction of 16% consisting of 27 SB2s, 2 SB3s and 1 SB4, increasing the number of known low-mass SBs by 50% and proving that strong X-ray emission is an extremely efficient way to find M-dwarf SBs. WASP photometry of 23 of these systems revealed two low-mass EBs, bringing the count of known M dwarf EBs to 15. BD -22 5866, the SB4, is fully described in Shkolnik et al. 2008 and CCDM J04404+3127 B consists of a two mid-M stars orbiting each other every 2.048 days. WASP also provided rotation periods for 12 systems, and in the cases where the synchronization time scales are short, we used P_rot to determine the true orbital parameters. For those with no P_rot, we use differential radial velocities to set upper limits on orbital periods and semi-major axes. More than half of our sample has near-equal-mass components (q > 0.8). This is expected since our sample is biased towards tight orbits where saturated X-ray emission is due to tidal spin-up rather than stellar youth. Increasing the samples of M dwarf SBs and EBs is extremely valuable in setting constraints on current theories of stellar multiplicity and evolution scenarios for low-mass multiple systems.Comment: Accepted to Ap

X-ray emission from the young brown dwarfs of the Taurus Molecular Cloud

The XMM-Newton Extended Survey of the TMC (XEST) is a large program designed to systematically investigate the X-ray properties of young stellar/substellar objects in the TMC. In particular, the area surveyed by 15 XMM-Newton pointings (of which three are archival observations), supplemented with one archival Chandra observation, allows us to study 17 BDs with M spectral types. Half of this sample (9 out of 17 BDs) is detected; 7 BDs are detected here for the first time in X-rays. We observed a flare from one BD. We confirm several previous findings on BD X-ray activity: a log-log relation between X-ray and bolometric luminosity for stars (with L*<10 Lsun) and BDs detected in X-rays; a shallow log-log relation between X-ray fractional luminosity and mass; a log-log relation between X-ray fractional luminosity and effective temperature; a log-log relation between X-ray surface flux and effective temperature. We find no significant log-log correlation between the X-ray fractional luminosity and EW(Halpha). Accreting and nonaccreting BDs have a similar X-ray fractional luminosity. The median X-ray fractional luminosity of nonaccreting BDs is about 4 times lower than the mean saturation value for rapidly rotating low-mass field stars. Our TMC BDs have higher X-ray fractional luminosity than BDs in the Chandra Orion Ultradeep Project. The X-ray fractional luminosity declines from low-mass stars to M-type BDs, and as a sample, the BDs are less efficient X-ray emitters than low-mass stars. We thus conclude that while the BD atmospheres observed here are mostly warm enough to sustain coronal activity, a trend is seen that may indicate its gradual decline due to the drop in photospheric ionization degree (abridged).Comment: 20 pages and 19 Figures. Accepted by A&A, to appear in a special section/issue dedicated to the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST). Preprint with higher resolution figures is available at http://hal.ccsd.cnrs.fr/ccsd-0009049