SAO 23229: A New Double-Lined Spectroscopic Eclipsing Binary

The discovery of eclipses of the bright star SAO 23229 (HD 14384; V=6.9; Spectral Type F5 V) by Indiana observer Dan Kaiser was described in a recent article in Sky and Telescope magazine (MacRobert, 1990). Photoelectric observations by H. Landis and D. Williams, reproduced in that article, show eclipses of 0.55 mag depth and period of 2.111 days. No secondary eclipses are reported, leaving open the question of whether the system contains a very dim secondary or whether it consists of two identical stars with an actual period of 4.2 days. We report here observations that favor the latter interpretation. [excerpt

Spectroscopic Binaries, Velocity Jitter, and Rotation in Field Metal-poor Red Giant and Red Horizontal-Branch Stars

We summarize 2007 radial velocity measurements of 91 metal-poor field red giants. Excluding binary systems with orbital solutions, our coverage averages 13.7 yr per star, with a maximum of 18.0 yr. We report four significant findings. (1) Sixteen stars are found to be spectroscopic binaries, and we present orbital solutions for 14 of them. The spectroscopic binary frequency of the metal-poor red giants, with [Fe/H] ≤ -1.4, for periods less than 6000 days, is 16% ± 4%, which is not significantly different from that of comparable-metallicity field dwarfs, 17% ± 2%. The two CH stars in our program, BD -1°2582 and HD 135148, are both spectroscopic binaries. (2) Velocity jitter is present among about 40% of the giants with MV ≤ -1.4. The two best-observed cases, HD 3008 and BD +22°2411, show pseudoperiodicities of 172 and 186 days, longer than any known long-period variable in metal-poor globular clusters. Photometric variability seen in HD 3008 and three other stars showing velocity jitter hints that starspots are the cause. However, the phasing of the velocity data with the photometry data from Hipparcos is not consistent with a simple starspot model for HD 3008. We argue against orbital motion effects and radial pulsation, so rotational modulation remains the best explanation. The implied rotational velocities for HD 3008 and BD +22°2411, both with MV ≤ -1.4 and R ≈ 50 R⊙, exceed 12 km s-1. (3) Including HD 3008 and BD +22°2411, we have found signs of significant excess line broadening in eight of the 17 red giants with MV ≤ -1.4, which we interpret as rotation. In three cases, BD +30°2034, CD -37°14010, and HD 218732, the rotation is probably induced by tidal locking between axial rotation and the observed orbital motion with a stellar companion. But this cannot explain the other five stars in our sample that display signs of significant rotation. This high frequency of elevated rotational velocities does not appear to be caused by stellar mass transfer or mergers: there are too few main-sequence binaries with short enough periods. We also note that the lack of any noticeable increase in mean rotation at the magnitude level of the red giant branch luminosity function "bump" argues against the rapid rotation's being caused by the transport of internal angular momentum to the surface. Capture of a planetary-mass companion as a red giant expands in radius could explain the high rotational velocities. (4) We also find significant rotation in at least six of the roughly 15 (40%) red horizontal-branch stars in our survey. It is likely that the enhanced rotation seen among a significant fraction of both blue and red horizontal-branch stars arose when these stars were luminous red giants. Rapid rotation alone therefore appears insufficient cause to populate the blue side of the horizontal branch. While the largest projected rotational velocities seen among field blue and red horizontal-branch stars are consistent with their different sizes, neither are consistent with the large values we find for the largest red giants. This suggests that some form of angular momentum loss (and possibly mass loss) has been at work. Also puzzling is the apparent absence of rotation seen in field RR Lyrae variables. Angular momentum transfer and conservation in evolved metal-poor field stars thus pose many interesting questions for the evolution of low-mass stars

Studies of multiple stellar systems - IV. The triple-lined spectroscopic system Gliese 644

We present a radial-velocity study of the triple-lined system Gliese 644 and derive spectroscopic elements for the inner and outer orbits with periods of 2.9655 and 627 days. We also utilize old visual data, as well as modern speckle and adaptive optics observations, to derive a new astrometric solution for the outer orbit. These two orbits together allow us to derive masses for each of the three components in the system: M_A = 0.410 +/- 0.028 (6.9%), M_Ba = 0.336 +/- 0.016 (4.7%), and $M_Bb = 0.304 +/- 0.014 (4.7%) M_solar. We suggest that the relative inclination of the two orbits is very small. Our individual masses and spectroscopic light ratios for the three M stars in the Gliese 644 system provide three points for the mass-luminosity relation near the bottom of the Main Sequence, where the relation is poorly determined. These three points agree well with theoretical models for solar metallicity and an age of 5 Gyr. Our radial velocities for Gliese 643 and vB 8, two common-proper-motion companions of Gliese 644, support the interpretation that all five M stars are moving together in a physically bound group. We discuss possible scenarios for the formation and evolution of this configuration, such as the formation of all five stars in a sequence of fragmentation events leading directly to the hierarchical configuration now observed, versus formation in a small N cluster with subsequent dynamical evolution into the present hierarchical configuration.Comment: 17 pages, 9 figures, Accepted for publication in MNRA

A Survey of Proper-Motion Stars. XVI. Orbital Solutions for 171 Single-lined Spectroscopic Binaries

We report 25,563 radial velocity measurements for 1359 single-lined stars in the Carney-Latham sample of 1464 stars selected for high proper motion. For 171 of these, we present spectroscopic orbital solutions. We find no obvious difference between the binary characteristics in the halo and the disk populations. The observed frequency is the same, and the period distributions are consistent with the hypothesis that the two sets of binaries were drawn from the same parent population. This suggests that metallicity in general, and radiative opacities in particular, have little influence over the fragmentation process that leads to short-period binaries. All the binaries with periods shorter than 10 days have nearly circular orbits, while the binaries with periods longer than 20 days exhibit a wide range of eccentricities and a median value of 0.37. For the metal-poor high-velocity halo binaries in our sample, the transition from circular to eccentric orbits appears to occur at about 20 days, supporting the conclusion that tidal circularization on the main sequence is important for the oldest binaries in the Galaxy

A Survey of Proper-Motion Stars. XV. Orbital Solutions for 34 Double-lined Spectroscopic Binaries

We present orbital solutions for 34 double-lined spectroscopic binaries found in the Carney-Latham sample of 1464 stars selected for high proper motion. We use TODCOR, a two-dimensional correlation technique, to extract the velocities for the primary and secondary stars and their light ratio. For our single-order echelle spectra, obtained with the Center for Astrophysics Digital Speedometers, we find that we can reach secondaries that are as much as 2 mag fainter than their primaries. The ratio of the primary to secondary velocity residuals from the orbital fit equals approximately the secondary-to-primary light ratio, as would be expected for the photon-limited case. We use our mass and light ratios to evaluate the mass-luminosity relation for metal-poor main-sequence dwarfs in the mass range 0.55–0.8 M. We assume an L ∝ β relation and find that the exponent at around 5200 Å is 7.4 ± 0.6. We find this is in good agreement with the slope of the corresponding theoretical MV- 14 Gyr isochrones from the VandenBerg & Bell models for metal-poor stars

Targeted and all-sky search for nanosecond optical pulses at Harvard-Smithsonian

We have built a system to detect nanosecond pulsed optical signals from a target list of some 10,000 sun-like stars, and have made some 20,000 observations during its two years of operation. A beamsplitter feeds a pair of hybrid avalanche photodetectors at the focal plane of the 1.5m Cassegrain at the Harvard/Smithsonian Oak Ridge Observatory (Agassiz Station), with a coincidence triggering measurement of pulse width and intensity at sub-nanosecond resolution. A flexible web-enabled database, combined with mercifully low background coincidence rates (approximately 1 event per night), makes it easy to sort through far-flung data in search of repeated events from any candidate star. An identical system will soon begin observations, synchronized with ours, at the 0.9m Cassegrain at Princeton University. These will permit unambiguous identification of even a solitary pulse. We are planning an all-sky search for optical pulses, using a dedicated 1.8m f/2.4 spherical glass light bucket and an array of pixelated photomultipliers deployed in a pair of matched focal planes. The sky pixels, 1.5 arcmin square, tessellate a 1.6 by 0.2 degree patch of sky in transit mode, covering the Northern sky in approximately 150 clear nights. Fast custom IC electronics will monitor corresponding pixels for coincident optical pulses of nanosecond timescale, triggering storage of a digitized waveform of the light flash

Studies of multiple stellar systems - III. Modulation of orbital elements in the triple-lined system HD 109648

The triple-lined spectroscopic triple system HD 109648 has one of the shortest periods known for the outer orbit in a late-type triple, 120.5 days, and the ratio between the periods of the outer and inner orbits is small, 22:1. With such extreme values, this system should show orbital element variations over a timescale of about a decade. We have monitored the radial velocities of HD 109648 with the CfA Digital Speedometers for eight years, and have found evidence for modulation of some orbital elements. While we see no definite evidence for modulation of the inner binary eccentricity, we clearly observe variations in the inner and outer longitudes of periastron, as well as in the radial velocity amplitudes of the three components. The observational results, combined with numerical simulations, allow us to put constraints on the orientation of the orbits.Comment: 11 pages, 7 figures, accepted by MNRA

Line Broadening in Field Metal-poor Red Giant and Red Horizontal Branch Stars

We report 349 radial velocities for 45 metal-poor field red giant and red horizontal branch stars. We have have identified one new spectroscopic binary, HD 4306, and one possible such system, HD 184711. We also report 57 radial velocities for 11 of the 91 stars reported on previously by Carney et al. (2003). As was found in the previous study, radial velocity "jitter" is present in many of the most luminous stars. Excluding stars showing spectroscopic binary orbital motion, all 7 of the red giants with M(V) <= -2.0 display jitter, as well as 3 of the 14 stars with -2.0 <= M(V) <= -1.4. We have also measured line broadening in all of the new spectra, using synthetic spectra as templates. The most luminous red giants show significant line broadening, as do many of the red horizontal branch stars, and we discuss briefly possible causes.Comment: To appear in the Astronomical Journa