Sebastien Lepine

SPECTROSCOPY OF NEW HIGH PROPER MOTION STARS IN THE NORTHERN SKY. I. NEW NEARBY STARS, NEW HIGH-VELOCITY STARS, AND AN ENHANCED CLASSIFICATION SCHEME FOR M DWARFS

We define an enhanced spectral classification scheme for M dwarf stars and use it to derive spectral classification of 104 northern stars with proper motions larger than 05 yr-1 that we discovered in a survey of high proper motion stars at low Galactic latitudes. The final tally is as follows: 54 M dwarfs, 25 sdK and sdM subdwarfs, 14 esdK and esdM extreme subdwarfs, and 11 DA and DC white dwarfs. Among the most interesting cases, we find one star to be the coolest subdwarf ever reported (LSR 2036+5059, with spectral type sdM7.5), a new M9.0 dwarf only about 6 pc distant (LSR 1835+3259), and a new M6.5 dwarf only 7 pc from the Sun (LSR 2124+4003). Spectroscopic distances suggests that 27 of the M dwarfs, three of the white dwarfs, and one of the subdwarfs (LSR 2036+5059) are within 25 pc of the Sun, making them excellent candidates for inclusion in the solar neighborhood census. Estimated sky-projected velocities suggest that most of our subdwarfs and extreme subdwarfs have halo kinematics. We find that several white dwarfs and non–metal-poor M dwarfs also have kinematics consistent with the halo, and we briefly discuss their possible origin.

Wind Inhomogeneities in Wolf-Rayet Stars. III. Unusual Emission-Line Profile Variations in Velorum

We present very high resolution, very high signal-to-noise ratio spectra from the 3.6 m Canada- France-Hawaii telescope for the strong C III j5696 emission line in c2 Velorum, the brightest Wolf-Rayet (WR) star in the sky. From two nights of spectroscopic monitoring, we have detected line pro—le varia- tions (LPVs) in the form of moving emission features (subpeaks) on the broad, ii —at-topped ˇˇ underlying pro—le. We use the working model from the previous paper in this series to study these LPVs in terms of inhomogeneities in the radially expanding stellar wind. A comparison between simulations and the data suggests the variable subpeaks to consist of a superposition of two distinct components: (1) narrow- moving subpeaks with a mean line-of-sight velocity dispersion km s~1, and (2) broad-moving p m ^ 80 subpeaks with km s~1. Both narrow and broad subpeak components are seen to move system- p m ^ 200 atically in a direction from the line center (m \ 0) toward the line edges. This motion is found to be consistent with a radial wind expansion at a mean acceleration rate m s~2. The narrow a r \ 13 ^ 3 subpeaks are found to be similar to the stochastic subpeaks seen in the LPVs from several single and long-period binary WR stars. On the other hand, the broad features are reminiscent of the recurrent subpeaks observed in the LPVs from a few peculiar WR stars (HD 4004, HD 191765, and EZ CMa), although in c2 Vel, we —nd no evidence for a recurrent behavior. We investigate the possibility that, in c2 Vel, these broad variable subpeaks arise from the shock-cone region, at the interface where the wind from the WR star collides with that of its O companion. We —nd no convincing evidence to support this hypothesis, although we suspect that there could be a relation between the existence of broad LPV subpeaks and the presence of the more massive O companion.

New High Proper Motion Stars from the Digitized Sky Survey. I. Northern Stars with 0[farcs]5 [CLC]yr[/CLC][TSUP]−1[/TSUP] < μ < 2[farcs]0 [CLC]yr[/CLC][TSUP]−1[/TSUP] at Low Galactic Latitudes

We have conducted a systematic search for high proper motion stars in the Digitized Sky Survey, in the area of the sky north of -2.8 degrees in declination and within 25 degrees of the Galactic plane. Using the SUPERBLINK software, a powerful automated blink comparator developed by us, we have identified 601 stars in the magnitude range 9 20 yr-1), and five were missed because they were either too bright for SUPERBLINK to handle or they are in the immediate proximity of very bright stars. Only one of Luytens stars (LHS 1657) could not be recovered at all, even by visual inspection of the POSS plates, and is now suspected to be bogus. The very high success rate in the recovery by SUPERBLINK of faint Luyten stars suggests that our new survey of high proper motion stars is at least 99% complete for stars with proper motions 05 yr-1 < μ < 20 yr-1 down to R = 19. This paper includes a list of positions, proper motions, magnitudes, and finder charts for all the new high proper motion stars.

First Wavelet Analysis of Emission Line Variations in Wolf-Rayet Stars

The quantification of stochastic substructures seen propagating away from the centers of emission lines of Wolf-Rayet (WR) stars is extended using the powerful, objective technique of wavelet analysis. Results for the substructures in one WR star so far show that the scaling laws between (a) flux and velocity dispersion and (b) lifetime and flux, combined with (c) their mass spectrum, strongly support the hypothesis that we are seeing the high mass tail-end distribution of full-scale supersonic compressible turbulence in the winds. This turbulence sets in beyond a critical radius from the star and shows remarkable similarity to the hierarchy of cloudlets seen in giant molecular clouds and other components of the ISM.The velocity dispersion is larger on average for substructures (interpreted as density enhanced turbulent eddies) propagating towards or away from the observer, suggesting that the turbulence is anisotropic. This is not surprising, since the most likely force which drives the windand the ensuing turbulence alike, radiation pressure, is directed outwards in all directions from the star. It is likely that a similar kind of turbulence prevails in the winds of all hot stars, of which those of WR stars are the most extreme.The consequences of clumping in winds are numerous. One of the most important is the necessary reduction in the estimate of the mass-loss rates compared to smooth outflow models.

The TESS Input Catalog and Candidate Target List

An erratum for this article has been published in 2018 AJ 156 183, https://doi.org/10.3847/1538-3881/aade86

The unusual cataclysmic binary star RBS 0490 and the space density of cataclysmic variables

RBS (ROSAT Bright Source) 0490 is a cataclysmic variable star (CV) with unusually strong emission lines. The strength of the emission lines has led to a suggestion that the object is intrinsically faint and correspondingly nearby (~33 pc), which, if true, would strongly affect estimates of the CV space density. Here we report astrometry, filter photometry, and time-series spectroscopy of this object. The astrometry gives an absolute parallax πabs = 4.5 ± 1.5 mas and a relative proper motion of 102 mas yr–1. A Bayesian procedure gives a very uncertain distance estimate of d ~ 300 pc, and the small parallax alone implies d > 133 pc (at 2 standard deviations). The mean V magnitude is 17.4, which implies MV = 10.9 -5 log [d/(200 pc], neglecting extinction. At 200 pc, the space velocity would be over 90 km s–1 with respect to the local standard of rest. The time-series spectroscopy shows a possible emission-line radial velocity period near 46 minutes. This would be unusually short for an orbital period, and it may represent some other clock in the system.

Discovery of an Ultracool Subdwarf: LSR 1425+7102, the First Star with Spectral Type [CLC]sd[/CLC]M8.0

We report the discovery of the coolest subdwarf reported to date. The star LSR 1425+7102 was discovered in our survey for faint high proper motion stars in the northern sky. Follow-up spectroscopy revealed the star to be a very red object with the characteristic signature of M subdwarfs: strong CaH bands but relatively weaker TiO bands. The CaH molecular band at ≈6900 A is particularly strong. By extrapolating the empirical relationship between the strength of the CaH molecular band and that of the subdwarf subtype, we conclude that LSR 1425+7102 is the first star to be discovered with spectral type sdM8.0.

Wavelet analysis of Wolf-Rayet emission line variability:

A wavelet analysis technique is developed and used to study variable spectral features on top of broad emission lines in Wolf-Rayet stars. A decomposition of the signal in discrete structures allows one to look for scaling laws. Results from the study of two Wolf-Rayet stars suggest we are seeing the upper tail-end of a scaled distribution. This provides a test for turbulence models, and sets new constraints on theoretical wind models.

Wavelet Analysis Of Wolf-Rayet Emission Line Variability: Evidence For Clumping

A wavelet analysis technique is developed and used to study variable spectral features on top of broad emission lines in Wolf-Rayet stars. A decomposition of the signal in discrete structures allows one to look for scaling laws. Results from the study of two Wolf-Rayet stars suggest we are seeing the upper tail-end of a scaled distribution. This provides a test for turbulence models, and sets new constraints on theoretical wind models.

Planet Candidates from K2 Campaigns 5–8 and Follow-up Optical Spectroscopy

We present 151 planet candidates orbiting 141 stars from K2 campaigns 5-8 (C5-C8), identified through a systematic search of K2 photometry. In addition, we identify 16 targets as likely eclipsing binaries, based on their light curve morphology. We obtained follow-up optical spectra of 105/141 candidate host stars and 8/16 eclipsing binaries to improve stellar properties and to identify spectroscopic binaries. Importantly, spectroscopy enables measurements of host star radii with