W. P. Chen

A lunar occultation and direct imaging survey of multiplicity in the Ophiuchus and Taurus star-forming regions

We present an IR lunar occultation and direct imaging search for companions in the Ophiuchus star-forming region and update a similar search of the Taurus region. The search is sensitive to companions in the angular separation range 0.005-10 sec. In Ophiuchus, we surveyed 35 young star targets; this sample contains at least 10 binaries, two triples, and one quadruple. Ten of the companion stars are newly discovered. In Taurus, the survey now includes 47 systems among which there are at least 22 binaries and four triples. Only two companion stars are newly identified because there is strong overlap with prior work. All the triples and quadruple are hierarchical. The observed binary frequency in Ophiuchus, in the 3-1400 AU range of separations, is at least 1.1 +/- 0.3 that of the nearby solar-like stars. This value is a lower bound because we make no corrections for incompleteness. In Taurus, in the same range of separations, the observed binary frequency is at least 1.6 +/- 0.3 that of the nearby solar-like stars. This value extends Ghez et al.s (1993) and Leinerts et al.s (1993) determination of an excess binary frequency to 3 AU separation. We used the weak-line T Tauri star/T Tauri star (WT/TT) type and the K-L color index to distinguish between systems with and without inner disks. We find no convincing difference in the binary frequency or distribution of separations of the systems with and without inner disks. The 1.3 mm continuum emission of the single systems exceeds that of the multiples suggesting that their extensive outer disks are more massive. The specific angular momenta of the binaries overlap those of molecular cloud cores measured by Goodman et al. (1993).

Deep wide-field spectrophotometry of the open cluster M67

We present nine color CCD intermediate-band spectrophotometry of a two square degree field centered on the old open cluster M67, from 3890

Microwave Spectra of 11 Polyyne Carbon Chains

\rm \AA

The unprecedented optical outburst of the quasar 3C 454.3 : The WEBT campaign of 2004-2005

to nearly 1

Multiplicity among the young stars in Taurus

\mu

Deep Intermediate-Band Surface Photometry of NGC 5907

. These observations are taken as a part of the BATC (Beijing-Arizona-Taipei-Connecticut) Color Survey of the Sky, for both scientific and calibration reasons. With these data we show that the BATC survey can reach its goal of obtaining spectrophotometry to a zero point accuracy of 0.01 mag, and down to V = 21 with 0.3 mag random error. We fit the color-magnitude diagrams (CMDs) with Wortheys theoretical models. The net result is the excellent fit of the 4.0 Gyr, [Fe/H] =

A new activity phase of the blazar 3C 454.3. Multifrequency observations by the WEBT and XMM-Newton in 2007-2008

-0.10

MULTIWAVELENGTH OBSERVATIONS OF 3C 454.3. I. THE AGILE 2007 NOVEMBER CAMPAIGN ON THE “CRAZY DIAMOND”

model to our data, including a good fit to the main sequence (MS) turn-off. Our data are consistent with a toy model with 50\% of the stars in M67 being binaries and a random distribution of binary mass-ratios, although other models with different mass-ratio distributions cannot be ruled out. The spatial distribution and mass function (MF) of stars in M67 show marked effects of dynamical evolution and evaporation of stars from the cluster. Blue stragglers and binary stars are the most condensed within the cluster, with degree of condensation depending on mass.We find M67 to have an elongated shape, oriented at an angle of

Triggered Star Formation in the Orion Bright-rimmed Clouds

15^{\circ}

Another look at the BL Lacertae flux and spectral variability - Observations by GASP-WEBT, XMM-Newton, and Swift in 2008–2009

relative to the galactic plane. Within its tidal radius, the observed MF of M67 between 1.2