The Smallest Mass Ratio Young Star Spectroscopic Binaries

Using high resolution near-infrared spectroscopy with the Keck telescope, we have detected the radial velocity signatures of the cool secondary components in four optically identified pre-main-sequence, single-lined spectroscopic binaries. All are weak-lined T Tauri stars with well-defined center of mass velocities. The mass ratio for one young binary, NTTS 160905-1859, is M2/M1 = 0.18+/-0.01, the smallest yet measured dynamically for a pre-main-sequence spectroscopic binary. These new results demonstrate the power of infrared spectroscopy for the dynamical identification of cool secondaries. Visible light spectroscopy, to date, has not revealed any pre-main-sequence secondary stars with masses <0.5 M_sun, while two of the young systems reported here are in that range. We compare our targets with a compilation of the published young double-lined spectroscopic binaries and discuss our unique contribution to this sample.Comment: Accepted for publication in the April, 2002, ApJ; 6 figure

Frozen to death? -- Detection of comet Hale-Bopp at 30.7 AU

Comet Hale--Bopp (C/1995 O1) has been the single most significant comet encountered by modern astronomy, still having displayed significant activity at 25.7 AU solar distance in late 2007. It is a puzzling question when and where this activity will finally cease. Here we present new observations with the ESO 2.2m telescope at La Silla to check the activity of Hale--Bopp at 30.7 AU solar distance. On 2010-12-04, 26 CCD images were taken with 180 s exposure times for photometry and morphology. The comet was detected in R and had a total brightness of 23.3+-0.2 mag, referring to an absolute brightness of R(1,1,0)=8.3. The profile of the coma was star-like at a seeing of 1.9", without any evidence of a coma or tail extending farther than 2.5" (=55,000 km in projection) and exceeding 26.5 mag/arcs^2 surface brightness. The measured total brightness corresponds to a relative total reflecting surface, a_RC, of 485 km^2, nine times less than three years before. The calculated a_RC value would imply a nucleus with 60--65 km radius assuming 4% albedo. This size estimate is in significant contradiction with the previous results scattering around 35 km. Therefore we suggest that the comet may still be in a low-level activity, despite the lack of a prominent coma. Alternatively, if the nucleus is already dormant, the albedo should be as high as 13%, assuming a radius of 35 km. With this observation, Hale--Bopp has been the most distant comet ever observed, far beyond the orbit of Neptune.Comment: 4 pages, accepted by A&

The CFEPS Kuiper Belt Survey: Strategy and Pre-survey Results

We present the data acquisition strategy and characterization procedures for the Canada-France Ecliptic Plane Survey (CFEPS), a sub-component of the Canada-France-Hawaii Telescope Legacy Survey. The survey began in early 2003 and as of summer 2005 has covered 430 square degrees of sky within a few degrees of the ecliptic. Moving objects beyond the orbit of Uranus are detected to a magnitude limit of $m_R$=23 -- 24 (depending on the image quality). To track as large a sample as possible and avoid introducing followup bias, we have developed a multi-epoch observing strategy that is spread over several years. We present the evolution of the uncertainties in ephemeris position and orbital elements as the objects progress through the epochs. We then present a small 10-object sample that was tracked in this manner as part of a preliminary survey starting a year before the main CFEPS project. We describe the CFEPS survey simulator, to be released in 2006, which allows theoretical models of the Kuiper Belt to be compared with the survey discoveries since CFEPS has a well-documented pointing history with characterized detection efficiencies as a function of magnitude and rate of motion on the sky. Using the pre-survey objects we illustrate the usage of the simulator in modeling the classical Kuiper Belt.Comment: to be submitted to Icaru

[Fe II] and H2 filaments in the Supernova Remnant G11.2-0.3: Supernova Ejecta and Presupernova Circumstellar Wind

We present the results of near-infrared imaging and spectroscopic observations of the young, core-collapse supernova remnant (SNR) G11.2-0.3. In the [Fe II] 1.644 um image, we first discover long, clumpy [Fe II] filaments within the radio shell of the SNR, together with some faint, knotty features in the interior of the remnant. We have detected several [Fe II] lines and HI Br-G line toward the peak position of the bright southeastern [Fe II] filament. The derived extinction is large (Av=13 mag) and it is the brightest [Fe II] filament detected toward SNRs to date. By analyzing two [Fe II] 1.644 um images obtained in 2.2 yrs apart, we detect a proper motion corresponding to an expansion rate of 0.''035 (0.''013) /yr [or 830 (310) km/s]. We also discover two small H2 filaments. One is bright and along the SE boundary of the radio shell, while the other is faint and just outside of its NE boundary. We have detected H2 (2-1) S(3) line toward the former filament and derive an excitation temperature of 2,100 K. We suggest that the H2 filaments are dense clumps in a presupernova circumstellar wind swept up by the SNR shock while the [Fe II] filaments are probably composed of both shocked wind material and shocked supernova (SN) ejecta. The distribution of [Fe II] filaments may indicate that the SN explosion in G11.2-0.3 was asymmetric as in Cassiopeia A. Our results support the suggestion that G11.2-0.3 is a remnant of a SN IIL/b interacting with a dense red supergiant wind.Comment: 30 pages with 10 figures, To appear in the Astrophysical Journa

An Association in the Aquila Star-Forming Region: High Resolution Infrared Spectroscopy of T Tauri Stars

We present the properties of a group of young stars associated with the well-studied T Tauri star system AS 353, located in the Aquila star-forming region. The association is identified using radial velocity measurements of sample objects selected from the Herbig and Bell Catalog based on their spatial proximity to AS 353. Radial velocities of nine objects were measured from multi-epoch high-resolution (R~30,000) H-band spectra obtained with NIRSPEC on Keck II. High-resolution K-band spectra were also obtained for most of the sample objects. Spectral types and rotational velocities are determined for all objects in the sample. The multi-epoch H-band spectra were examined for radial velocity variations in order to detect possible spectroscopic binaries. Eight of the nine objects have radial velocities that are consistent within the 1-sigma scatter of the sample. From their mean of -8.6 km/s these eight objects have a standard deviation of 2 km/s, which suggests that the sample stars are related. The ninth object shows significant radial velocity variations between epochs, characteristic of a spectroscopic binary. The overall multiplicity of the sample is high; we observed 13 stars in seven systems, identifying three new candidate binary components in this project. Many of the spectra reveal hydrogen emission lines typical of strong accretion processes, indicating that most of these objects harbor circumstellar disks and are less than a few million years old. We discuss possible interpretations of the enigmatic pure emission line spectrum of HBC 684. This work represents the highest spectral resolution infrared observations to date of these intriguing, nearby young stars.Comment: 7 figures, accepted to Astrophysical Journa

An Upper Bound on the Flux Ratio of rho CrB's Companion at 1.6um

We use high resolution infrared spectroscopy to investigate the 2001 report by Gatewood and colleagues that rho CrB's candidate extrasolar planet companion is really a low-mass star with mass 0.14+-0.05 Msun. We do not detect evidence of such a companion; the upper bounds on the (companion/primary) flux ratio at 1.6 microns are less than 0.0024 and 0.005 at the 90 and 99% confidence levels, respectively. Using the H-band mass-luminosity relationship calculated by Baraffe and colleagues, the corresponding upper limits on the companion mass are 0.11 and 0.15 Msun. Our results indicate that the infrared spectroscopic technique can detect companions in binaries with flux ratios as low as 0.01 to 0.02.Comment: 22 pages, 10 figures, accepted for publication in the Astronomical Journa

A multiwavelength approach to the SFR estimation in galaxies at intermediate redshifts

We use a sample of 7 starburst galaxies at intermediate redshifts (z ~ 0.4 and z ~ 0.8) with observations ranging from the observed ultraviolet to 1.4 GHz, to compare the star formation rate (SFR) estimators which are used in the different wavelength regimes. We find that extinction corrected Halpha underestimates the SFR, and the degree of this underestimation increases with the infrared luminosity of the galaxies. Galaxies with very different levels of dust extinction as measured with SFR(IR)/SFR(Halpha, uncorrected for extinction) present a similar attenuation A[Halpha], as if the Balmer lines probed a different region of the galaxy than the one responsible for the bulk of the IR luminosity for large SFRs. In addition, SFR estimates derived from [OII]3727 match very well those inferred from Halpha after applying the metallicity correction derived from local galaxies. SFRs estimated from the UV luminosities show a dichotomic behavior, similar to that previously reported by other authors in galaxies at z <~ 0.4. Here we extend this result up to z ~ 0.8. Finally, one of the studied objects is a luminous compact galaxy (LCG) that may be suffering similar dust-enshrouded star formation episodes. These results highlight the relevance of quantifying the actual L(IR) of LCGs, as well as that of a much larger and generic sample of luminous infrared galaxies, which will be possible after the launch of SIRTF.Comment: Accepted for publication in The Astrophysical Journa

Component Masses of the Young Spectroscopic Binary UZ Tau E

We report estimates of the masses of the component stars in the pre-main-sequence spectroscopic binary UZ Tau E. These results come from the combination of our measurements of the mass ratio, M2/M1=0.28 +/-0.01, obtained using high resolution H-band spectroscopy, with the total mass of the system, (1.31 +/-0.08)(D/140pc) M_sun, derived from millimeter observations of the circumbinary disk (Simon et al. 2000). The masses of the primary and secondary are (1.016 +/-0.065)(D/140pc) M_sun and (0.294 +/-0.027)(D/140pc) M_sun, respectively. Using the orbital parameters determined from our six epochs of observation, we find that the inclination of the binary orbit, 59.8 +/-4.4 degrees, is consistent with that determined for the circumbinary disk from the millimeter observations, indicating that the disk and binary orbits are probably coplanar.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter

Children with mixed developmental language disorder have more insecure patterns of attachment.

Developmental Language disorders (DLD) are developmental disorders that can affect both expressive and receptive language. When severe and persistent, they are often associated with psychiatric comorbidities and poor social outcome. The development of language involves early parent-infant interactions. The quality of these interactions is reflected in the quality of the child's attachment patterns. We hypothesized that children with DLD are at greater risk of insecure attachment, making them more vulnerable to psychiatric comorbidities. Therefore, we investigated the patterns of attachment of children with expressive and mixed expressive- receptive DLD. Forty-six participants, from 4 years 6 months to 7 years 5 months old, 12 with expressive Specific Language Impairment (DLD), and 35 with mixed DLD, were recruited through our learning disorder clinic, and compared to 23 normally developing children aged 3 years and a half. The quality of attachment was measured using the Attachment Stories Completion Task (ASCT) developed by Bretherton. Children with developmental mixed language disorders were significantly less secure and more disorganized than normally developing children. Investigating the quality of attachment in children with DLD in the early stages could be important to adapt therapeutic strategies and to improve their social and psychiatric outcomes later in life

A Multiplicity Census of Young Stars in Chamaeleon I

We present the results of a multiplicity survey of 126 stars spanning ~0.1-3 solar masses in the ~2-Myr-old Chamaeleon I star-forming region, based on adaptive optics imaging with the ESO Very Large Telescope. Our observations have revealed 30 binaries and 6 triples, of which 19 and 4, respectively, are new discoveries. The overall multiplicity fraction we find for Cha I (~30%) is similar to those reported for other dispersed young associations, but significantly higher than seen in denser clusters and the field, for comparable samples. Both the frequency and the maximum separation of Cha I binaries decline with decreasing mass, while the mass ratios approach unity; conversely, tighter pairs are more likely to be equal mass. We confirm that brown dwarf companions to stars are rare, even at young ages at wide separations. Based on follow-up spectroscopy of two low-mass substellar companion candidates, we conclude that both are likely background stars. The overall multiplicity fraction in Cha I is in rough agreement with numerical simulations of cloud collapse and fragmentation, but its observed mass dependence is less steep than predicted. The paucity of higher-order multiples, in particular, provides a stringent constraint on the simulations, and seems to indicate a low level of turbulence in the prestellar cores in Cha I.Comment: Accepted for publication in Ap