We report on the most sensitive water maser survey toward Bok globules to date, performed using NASA's 70m antenna at Robledo de Chavela (Spain). We observed 207 positions within the Clemens and Barvainis catalog with a higher probability of harboring a young star, using as selection criteria the presence of radio continuum emission (from submillimeter to centimeter wavelengths), geometric centers of molecular outflows, peaks in maps of high-density gas tracers (NH3 or CS), and IRAS point sources. We have obtained seven maser detections, six of which (in CB 34, CB 54, CB 65, CB 101, CB 199, and CB 232) are reported for the first time here. Most of the water masers we detected are likely to be associated with young stellar objects (YSOs), except for CB 101 (probably an evolved object) and CB 65 (uncertain nature). The water maser in CB 199 shows a relatively high shift (30km/s) of its velocity centroid with respect to the cloud velocity, which is unusual for low-mass YSOs. We speculate that high-velocity masers in this kind of object could be related to episodes of energetic mass loss in close binaries. Alternatively, the maser in CB 199 could be pumped by a protoplanetary or a young planetary nebula. CB 232 is the smallest Bok globule (0.6pc) known to be associated with water maser emission, although it would be superseded by the cases of CB 65 (0.3pc) and CB 199 (0.5pc) if their association with YSOs is confirmed. All our selection criteria have statistically compatible detection rates, except for IRAS sources, which tend to be somewhat worse predictors for the presence of maser emission.
This paper presents new results of a water maser survey of late-type stellar objects at 22.235GHz with the Kashima 34-m radio telescope. We have detected 179 out of 643 observed sources, including 32 new detections. The sources were selected in terms of the IRAS flux density and colors of late-type stars, involving optically observable Mira/semi-regular variables, IRC objects, OH/IR sources and proto-planetary nebulae. We found the highest H_2_O detection rate for the type of stars with a thin dust envelope (Mira/semi-regular variables) among other types of sources. This is attributed to the smaller distances to such stars in the sample. The velocity spread of the H_2_O maser profile has an increasing tendency with the IRAS color, though it becomes more difficult to access this color dependence beyond an edge of the transition of the (oxygen-rich) Asymptotic Giant Branch stars to protoplanetary nebulae in the two-color diagram.
High sensitivity observations of the 22GHz water maser emission have been carried out with the Effelsberg 100m radio telescope. The observed sample was 79 candidate high-mass protostellar objects from a flux-limited sample of 6.7GHz methanol sources (Szymczak et al., 2002A&A...392..277S). Water maser emission was found in 41 sources of which 28 were not previously catalogued.
Thorium-Argon lamps are commonly used as wavelength calibration units at moderately high spectral resolutions because of the richness of the thorium spectrum in the visual. The inclusion of blended lines whose position is assumed to coincide with the laboratory wavelength of the main component is shown to result in a calibration precision significantly worse than the intrinsic random noise limit. In order to avoid this degradation of the calibration, we present resolution-dependent Th-Ar wavelengths in the region 277 to >1000nm for use at pixel-scales (pixel-size expressed in wavelength units) between {lambda}/2.5x10+4 and {lambda}/10+5.
A collection of data for 115 extinction curves derived from low-dispersion IUE spectra are presented with normalization to E(B-V)=1. The electronic Atlas of Extinctions contains the list of the stars used, their association membership, and the normalized extinctions for 88 wavelength values between 1260 and 3000 Angstroems.
The supernova remnant (SNR) W49B originated from a core-collapse supernova that occurred between one and four thousand years ago, and subsequently evolved into a mixed-morphology remnant, which is interacting with molecular clouds (MC). Gamma-ray observations of SNR-MC associations are a powerful tool to constrain the origin of Galactic cosmic rays, as they can probe the acceleration of hadrons through their interaction with the surrounding medium and subsequent emission of non-thermal photons. We report the detection of a gamma-ray source coincident with W49B at very high energies (VHE; E>100GeV) with the H.E.S.S. Cherenkov telescopes together with a study of the source with five years of Fermi-LAT high-energy gamma-ray (0.06-300GeV) data. The smoothly connected, combined source spectrum, measured from 60MeV to multi-TeV energies, shows two significant spectral breaks at 304+/-20MeV and 8.4_-2.5_^+2.2^GeV; the latter is constrained by the joint fit from the two instruments. The detected spectral features are similar to those observed in several other SNR-MC associations and are found to be indicative of gamma-ray emission produced through neutral-pion decay.
The internal structure constants k_j_ and the radius of gyration are useful tools for investigating the apsidal motion and tidal evolution of close binaries and planetary systems. These parameters are available for various evolutionary phases but they are scarce for the late stages of stellar evolution. To cover this gap, we present here the calculations of the apsidal-motion constants, the fractional radius of gyration, and the gravitational potential energy for two grids of cooling evolutionary sequences of white dwarfs and for neutron star models. The cooling sequences of white dwarfs were computed with LPCODE. An additional alternative to the white dwarf models was also adopted with the MESA code which allows non-stop calculations from the pre main-sequence (PMS) to the white dwarf cooling sequences. Neutron star models were acquired from the NSCool/TOV subroutines. The apsidal-motion constants, the moment of inertia and the gravitational potential energy were computed with a fourth-order Runge-Kutta method. The parameters are made available for four cooling sequences of white dwarfs (DA and DB types): 0.52, 0.57, 0.837 and 1.0M_{sun}_ and for neutron star models covering a mass range from 1.0 up to 2.183M_{sun}_, in 0.1 mass step. We show that, contrary to previously established opinion, the product of the form-factors {beta} and {alpha}, which are related to the moment of inertia, and gravitational potential energy, is not constant during some evolutionary phases. Regardless of the final products of stellar evolution (white dwarfs, neutron stars and perhaps black holes), we found that they recover the initial value of product {alpha}{beta} at the pre main-sequence phase (~0.4). These results may have important consequences for the investigation of the Jacobi virial equation.
We present an activity and kinematic analysis of high proper motion white dwarf-M dwarf binaries (WD+dMs) found in the SUPERBLINK survey, 178 of which are new identifications. To identify WD+dMs, we developed a UV-optical-IR color criterion and conducted a spectroscopic survey to confirm each candidate binary. For the newly identified systems, we fit the two components using model white dwarf spectra and M dwarf template spectra to determine physical parameters. We use H{alpha} chromospheric emission to examine the magnetic activity of the M dwarf in each system, and investigate how its activity is affected by the presence of a white dwarf companion. We find that the fraction of WD+dM binaries with active M dwarfs is significantly higher than their single M dwarf counterparts at early and mid-spectral types. We corroborate previous studies that find high activity fractions at both close and intermediate separations. At more distant separations, the binary fraction appears to approach the activity fraction for single M dwarfs. Using derived radial velocities and the proper motions, we calculate 3D space velocities for the WD+dMs in SUPERBLINK. For the entire SUPERBLINK WD+dMs, we find a large vertical velocity dispersion, indicating a dynamically hotter population compared to high proper motion samples of single M dwarfs. We compare the kinematics for systems with active M dwarfs and those with inactive M dwarfs, and find signatures of asymmetric drift in the inactive sample, indicating that they are drawn from an older population.
The detection of a dust disk around the white dwarf star G29-38 and transits from debris orbiting the white dwarf WD 1145+017 confirmed that the photospheric trace metals found in many white dwarfs arise from the accretion of tidally disrupted planetesimals. The composition of these planetesimals is similar to that of rocky bodies in the inner Solar System. Gravitational scattering of planetesimals towards the white dwarf requires the presence of more massive bodies, yet no planet has so far been detected at a white dwarf. Here we report optical spectroscopy of a hot (about 27750 kelvin) white dwarf, WD J091405.30+191412.25, that is accreting from a circumstellar gaseous disk composed of hydrogen, oxygen and sulfur at a rate of about 3.3x10<SUP>9</SUP> grams per second. The composition of this disk is unlike all other known planetary debris around white dwarfs, but resembles predictions for the makeup of deeper atmospheric layers of icy giant planets, with H<SUB>2</SUB>O and H<SUB>2</SUB>S being major constituents. A giant planet orbiting a hot white dwarf with a semi-major axis of around 15 solar radii will undergo substantial evaporation with expected mass loss rates comparable to the accretion rate that we observe onto the white dwarf. The orbit of the planet is most probably the result of gravitational interactions, indicating the presence of additional planets in the system. We infer an occurrence rate of approximately 1 in 10000 for spectroscopically detectable giant planets in close orbits around white dwarfs.
