Galactic Dark Clouds Research Articles

New Herbig–Haro objects associated with embedded sources

ABSTRACT We continue to present the results of the Byurakan Narrow Band Imaging Survey (BNBIS). The main goal of this survey is to search for Herbig–Haro (HH) objects and jets in Galactic dark clouds. In this work we present the results of the search in the vicinity of infrared sources that are bright in the WISE survey and embedded in the dark clouds. The survey is performed with the 1-m Schmidt telescope of Byurakan Observatory, lately equipped with a new CCD detector, which allows to obtain one square degree images of the sky in various filters. Narrow-band filters were used to obtain H α and [S ii] images, and a medium-width filter was used for the continuum imaging. New HH flows and knots were found near six embedded IR sources, which constitutes a significant proportion of the objects observed. At least two of the newly found HH flows (HH 1226 and HH 1227) lie in isolated dark clouds, thus pointing to active star formation in these regions. Other flows are also located in detached and dense globules or filaments. The length of the HH 1228 flow is about 1 pc; it has also a molecular hydrogen counterpart of the same extension. Coordinates, charts, detailed descriptions and distance estimates are provided. The lower limits of bolometric luminosities of the source stars are typical for low-mass young stellar objects.

Detection of deuterated molecules, but not of lithium hydride, in the z = 0.89 absorber toward PKS 1830−211

Deuterium and lithium are light elements of high cosmological and astrophysical importance. In this work we report the first detection of deuterated molecules and a search for lithium hydride, 7LiH, at redshift z = 0.89 in the spiral galaxy intercepting the line of sight to the quasar PKS 1830−211. We used ALMA to observe several submillimeter lines of ND, NH2D, and HDO, and their related isotopomers NH2, NH3, and H218O, in absorption against the southwest image of the quasar, allowing us to derive XD/XH abundance ratios. The absorption spectra mainly consist of two distinct narrow velocity components for which we find remarkable differences. One velocity component shows XD/XH abundances that is about 10 times larger than the primordial elemental D/H ratio, and no variability of the absorption profile during the time span of our observations. In contrast, the other component shows a stronger deuterium fractionation. Compared to the first component, this second component has XD/XH abundances that are 100 times larger than the primordial D/H ratio, a deepening of the absorption by a factor of two within a few months, and a rich chemical composition, with relative enhancements of N2H+, CH3OH, SO2 and complex organic molecules. We therefore speculate that this component is associated with the analog of a Galactic dark cloud, while the first component is likely more diffuse. Our search for the 7LiH (1–0) line was unsuccessful and we derive an upper limit 7LiH/H2 = 4 × 10−13 (3σ) in the z = 0.89 absorber toward PKS 1830−211. Besides, with ALMA archival data, we could not confirm the previous tentative detections of this line in the z = 0.68 absorber toward B 0218+357; we derive an upper limit 7LiH/H2 = 5 × 10−11 (3σ), although this is less constraining than our limit toward PKS 1830−211. We conclude that, as in the Milky Way, only a tiny fraction of lithium nuclei are possibly bound in LiH in these absorbers at intermediate redshift.

The new nebula in LDN 1415 – A cry from the cradle of a low-luminosity source

A survey for candidate Herbig-Haro objects was performed to search for evidence of star formation in Galactic dark clouds. For this aim true colour images were created from blue, red, and infrared DSS2 plates and inspected. Follow-up I-band, Halpha, and [SII] CCD imaging and long-slit spectroscopy using the Tautenburg 2-m telescope was carried out to verify candidate objects. In the case of LDN 1415, the presence of a Herbig-Haro flow could be revealed which is henceforth named HH 892. In addition, an arcuate nebula was found which is barely seen on the DSS2 infrared plate (epoch 1996) and not detected in archival Kiso Schmidt data (epoch 2001). Thus, this nebula must have brightened by about 3.8mag in recent years.The nebula is associated with IRAS 04376+5413. The 2MASS images show a red counterpart of the IRAS source, designated as L1415-IRS. Its morphology resembles that of a bipolar young object. The luminosity of this source integrated from 0.9micron to 60micron in the low state amounts to 0.13L_sun for an assumed distance of 170pc. Thus it seems to be a young very-low mass star or it might even be of substellar mass. The current brightness increase of the nebula is caused by a FUor- or EXor-like outburst as indicated by the presence of a P Cygni profile of the Halpha line. L1415-IRS is by far the least luminous member of the sparse sample of FUor and EXor objects.

New M-Type Variables in Galactic Dark Clouds

We present the results of the classification of newly discovered M-type variables obtained as part of an H-alpha survey of Galactic dark cloud regions.

New M-Type Variables in Galactic Dark Clouds

The results of the spectral classification of newly discovered M-type variables obtained as part of an H-alpha survey of Galactic dark cloud regions are presented. The survey was carried out with the 40″ Schmidt camera of Byurakan Observatory, and the spectra of the variable stars for the classification were obtained with the Observatory's 2.6-m telescope. The observational material allowed register of late M-type variables as well as their brightness variations. Among the 97 newly discovered M-type stars, 22 show brightness variations. The results of the spectral classification of these new variables show that 21 out of 22 are red giants, and in all probability they are Mira Ceti type long period variables.

Searching for old neutron stars with ROSAT

This is the second in a series of three papers constraining the number of detectable old neutron stars in the Galaxy. Here, I present the statistical analysis of a sample of X-ray sources coincident with areas of dark clouds in the Galactic plane. I compare this sample with all sources in the ROSAT All-Sky Survey bright source catalog within 20 of the Galactic plane. I present the re- sults of an identication program of a subset of sources that are compatible with a soft, thermal X-ray spectrum and an eective source temperature of less than 70 eV. The three brightest sources in this sample form an intriguing subgroup. One of them is a previously identied candi- date for an accreting neutron star. I identify the other two sources with hot white dwarf stars. I nd no new ac- creting neutron star candidate in this sample. Based on this result, I derive an upper limit to the space density of accreting neutron stars in elds of Galactic dark clouds of 2s r 1 at a count rate > 0:05 s 1 .

Redshifted Molecular Absorption Systems toward PKS 1830−211 and B0218+357: Submillimeter CO, C [CSC]i[/CSC], and H[TINF]2[/TINF]O Data

We have detected the J=4←3 rotational transition of 12CO in absorption at z = 0.89 toward the quasar PKS 1830-211, but not the 12CO (5←4) or the 3P1←3P0 fine-structure line of neutral carbon. The intervening molecular medium thus has a total 12CO column density of 1018 cm−2≤N(CO)≤5×1018 cm-2 with a most likely value of N(CO)≃2×1018 cm-2, which corresponds to the large column density of molecular hydrogen of N(H2)=2.5×1022 cm-2 and a reddening of Av = 25 mag. The 12CO excitation temperature is low, below 15 K. Comparison with existing molecular absorption results shows that the absorbing material has molecular abundances similar to Galactic dark clouds. We find an upper limit for atomic carbon of N(C I)≤1018 cm-2, which again would be the case for most Galactic dark clouds.

The velocity gradient of B361

view Abstract Citations (9) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The velocity gradient of B361 Clark, F. O. ; Johnson, D. R. Abstract Observations of a well-ordered velocity gradient that decreases with decreasing cloud radius are reported for the galactic dark cloud B361. The source also exhibits systematic changes in spectral line width. Current observations confirm the suggestion of rotation in this source reported earlier and imply the presence of an effective mechanism for redistributing angular momentum. Magnetic braking is invoked to explain the observed effects. Publication: The Astrophysical Journal Pub Date: December 1982 DOI: 10.1086/160491 Bibcode: 1982ApJ...263..160C Keywords: Gas Dynamics; Interstellar Gas; Nebulae; Velocity Distribution; Angular Momentum; Formaldehyde; Gas Density; Hydroxyl Radicals; Magnetic Effects; Velocity Measurement; Astrophysics full text sources ADS |

New H? emission stars in galactic dark clouds

New H? emission stars in galactic dark clouds

On continuum radiation from dark clouds.

Surveys of galactic dark clouds at 5.0 and 7.8 GHz have no detections with flux density approximately-greater-than0.2 Jy. A model of continuum emission from H II and C II regions surrounding embedded stars indicates that, in most dark clouds, no young stars earlier than B1 are likely to be present. Application of the model to detections in the rho Ophiuchi cloud indicates that the extended source due to the B2 star HD 147889 may have expansion age 10/sup 5/ yr; the smaller sources may be due to B3 stars, with expansion ages 10/sup 3/ yr. The younger sources are associated with a greater density of gas and dust.