Search for HH objects and emission stars in star formation regions. IV. New Herbig-Haro flows and objects associated with cometary nebulae

As part of a project to search for new Herbig-Haro (HH) objects in star formation regions, observations are reported on the neighborhoods of five cometary nebulae: MacC H12, MacC sH15, GM 1-14, RNO 33, and Pars 17. We have been able to identify 9 previously unknown HH objects in those regions. Almost all of these objects belong to directed flows whose sources are, with high probability, the central stars of these nebulae. In the cases of MacC H12 and GM 1-14, the outflows have a distinct bipolar structure. The sources of the outflows are located on a J-H/H-K diagram in order to classify them. __________ Translated from Astrofizika, Vol. 51, No. 1, pp. 15–27 (February 2008).     

The compact nebulae cn1 and cn2, coupled to infrared stellar clusters

This is a study of the compact nebulae cn1 and cn2 situated in the extended, bright nebula S235. ¹²CO observations reveal the presence of blue and red outflows (i.e., a bipolar outflow) from the molecular cloud in which these nebulae are embedded. cn1 and cn2 are shown to be coupled to IR clusters of young stars, some of which have dust disks or envelopes (these are so-called young stellar objects, YSOs), with the YSOs grouped around the center of the clusters. cn1 is coupled to the infrared point source IRAS05377 + 3548, whose IR colors are close to those of T Tau stars. A chain of objects emerging from S235 (which clearly implies they are coupled in terms of evolution) is studied. These are the compact nebulae S235 A, B, and C, and the Herbig-Haro objects GGD5 and GGD6. A group of IR stars associated with GGD6 is also studied.     

Searches for HH objects and emission stars in star formation regions. V. Two new cometary nebulae in Perseus

A small region surrounding the emission star LkHα 326 in the Perseus dark cloud is studied in the optical range. Two new cometary nebulae are described and their relationship to the Herbig-Haro objects in this region is examined. An HH-jet is discovered near the central star of one of these nebulae. Six emission stars, of which four are new, are detected by slitless spectroscopy. __________ Translated from Astrofizika, Vol. 51, No. 2, pp. 219–228 (May 2008).     

Star formation and molecular clouds

The hypothesis advanced by V. A. Ambartsumyan according to which stars are formed from prestellar superdense objects-- protostars-- was an alternative to the hypothesis of the 1950's (and even now, not much changed) according to which stars are formed by accretion with subsequent collapse (in various modifications). Ambartsumyan's basic inferences were based on an analysis of the observational data available at that time. This paper presents both Ambartsumyan's pioneering ideas and some modern hypotheses of star formation. Some results from studies of molecular clouds and star formation regions are also discussed. One of the distinctive features of young stellar objects (YSO) is the outflow of matter from these objects (molecular, in the form of jets, etc.), a phenomenon whose importance for the evolution of stars was noted by Ambartsumyan as long ago as 1937. Radial systems of dark globules are examined, as well as H-H objects associated with star formation regions, cometary nebulae, and close Trapeziumtype systems (consisting of YSO). Translated from Astrofizika, Vol. 52, No. 2, pp. 185–202 (May 2009).     

Searches for HH-objects and Emission Stars in Star Formation Regions. II. The Region of GM1-61 and V453 Ori

Observations of objects lying in the dark cloud L1582A, which contains the cometary nebulae GM1-61 and V453 Ori, are reported. Five previously unknown HH-objects are discovered in this region; they appear to form several flows. The morphology of the nebulae is examined and possible sources of the HH-flows are discussed. Another reflecting nebula is found that is visible mainly in the infrared.     

Infrared Study of T Tauri Stars Based on IRAS and 2MASS Observations

The IRAS and 2MASS associations for 193 T Tauri stars are identified in this paper. From the color–color diagrams and spectral index, it is found that the IR excesses for most samples are due to thermal emission from the circumstellar material, as suggested previously. It is also found that the IR excesses at IRAS region for few T Tauri stars and the near-IR excesses for some T Tauri stars are likely attributed to free-free emission or free-bound emission from the circumstellar ionized gas. Moreover, It is found in deredened J–H versus H–K color–color diagram that there is a slight separation in different spectral groups. The T Tauri stars locus equation in J–H versus H–K color–color diagram for our sample is also presented.     

First Byurakan Spectral Sky Survey. Stars of late spectral types. −11° ≤ δ ≤ −7° belt

A 10th list of late-type M and C stars found on plates of the First Byurakan Spectral Sky Survey in the − 11° ≤ δ ≤ − 7° belt with an area of about 1070 deg² is given. The list contains data on 169 red stars, 117 of which were found for the first time: 8 are new C stars, 3 are Cstar candidates, 104 are M stars, 1 is either an M or an S star, and 1 object on the survey plate cannot be classified. Of the 117 objects, 47 are unidentified IRAS sources. A statistical analysis of the objects that are and are not identified with IRAS sources shows that the identified stars are, with a high probability, brighter and have relatively more massive envelopes. Two stars were found to have fairly large brightness variability (with an amplitude of at least 6^m.O). Gasdust shells are assumed to exist around nine of the IRAS sources. The equatorial coordinates, spectral types, and stellar magnitudes, determined on Palomar E maps, are given for the selected objects. Translated from Astrofizika, Vol. 41. No. 4, pp. 545–559, October–December, 1998.     

New OB-association in Pup — CMa

A new method of determination of distances to stellar associations is proposed. This method is based on the measurements of mean thicknesses of globules of the systems of dark globules connected with that association. It is shown that the method is in good agreement with other known methods. A new grouping of OB stars in Pup-CMa is found. It is shown that this grouping has properties characteristic for OB-associations: the stars of that grouping have similar distances, similar radial velocities, the grouping is connected with molecular clouds, with Herbig-Haro objects, and cometary nebulae. All these results are in favour of this grouping to be a new OB-association. We named that association OB-association Pup-CMa. The preliminary results of¹²CO observations of molecular clouds connected with that association are also given. The radial velocities of these clouds are in good agreement with the mean radial velocity of stars in the association in Pup-CMa. Translated from Astrofizika, Vol. 42, No. 2, pp. 179–188, April–June, 1999.     

Optical identification of 100 IRAS Point Sources at high galactic latitude

The low-dispersion spectra of the First Byurakan Survey and the red and blue images of the Palomar Observatory Sky Survey have been used to identify optically 100 infrared sources from the IRAS Point Source Catalog. The work was carried out over the region 3^h 50^m ≤ α ≤ 7^h 40^m and +69° ≤ δ −73° with an area of 75 square degrees. The optical coordinates, their deviations from the infrared coordinates, V magnitudes, color indices, preliminary classes for all the objects, and a number of remarks on interesting objects are presented. Three objects were found to be quasars, 36 are galaxies (including Seyferts and an interacting pair), 5 are faint planetary nebulae, 9 are carbon stars, and 47 are stars of late M subclasses. Translated fromAstrofizika, Vol. 40, No. 1, pp. 5–18, February, 1997.     

Optical identifications of iras point sources based on low-dispersion fbs spectra. Stars. IV

A fourth list of point sources from the IRAS Point Source Catalog (PSC) that are optically identified with stars of late spectral types is given. The list contains data on 41 objects. The identifications were based on the Digital Sky Survey (DSS), the First Byurakan Survey, blue and red maps of the Palomar Observatory Sky Survey, and infrared fluxes at the wavelengths 12, 25, 60, and 100 μm in the region of +65° ≤ δ ≤ +69° and 05^h10^m ≤ α ≤ 18^h10^m. Of the 41 objects, which are given in the IRAS PSC as unidentified sources of infrared emission, 9 are associated with known stars in existing catalogs while 32 sources remained unidentified in the optical range, one of which is also a source in the deep IRAS survey (IRAS Serendipitous Source Catalog). The optical coordinates, their departures from the IR coordinates, the V stellar magnitudes, the color indices CI, and the preliminary spectral subtypes have been determined. The objects have optical magnitudes in the range of 8^m.5-14^m.5. Finder charts from the DSS are given for 32 of the objects. Translated from Astrofizika, Vol. 43, No. 3, pp. 361-368, July–September, 2000.     

Spectral observations of stars associated with nebulae. I. PP52, PP57, PP63, and PP89

Spectral observations of stars associated with nebulae, PP52, PP57, PP63, and PP89, are reported. The star PP52 is of spectral type A and is associated with a reflecting nebula. PP57 is a nonstationary star. A weak object (1079-0122733) immediately adjacent to PP57 is highly variable. It is shown that the nebulae PP63 and PP89 are cometary. __________ Translated from Astrofizika, Vol. 49, No. 1, pp. 61–69 (February 2006).     

Studies of ultracompact H ii regions — II. High-resolution radio continuum and methanol maser survey

High spatial resolution radio continuum and 6.67-GHz methanol spectral line data are presented for methanol masers previously detected by Walsh et al. (1997). Methanol maser and/or radio continuum emission is found in 364 cases towards IRAS -selected regions. For those sources with methanol maser emission, relative positions have been obtained to an accuracy of typically 0.05 arcsec, with absolute positions accurate to around 1 arcsec. Maps of selected sources are provided. The intensity of the maser emission does not seem to depend on the presence of a continuum source. The coincidence of water and methanol maser positions in some regions suggests there is overlap in the requirements for methanol and water maser emission to be observable. However, there is a striking difference between the general proximity of methanol and water masers to both cometary and irregularly shaped ultracompact (UC) H  ii regions, indicating that, in other cases, there must be differing environments conducive to stimulating their emission. We show that the methanol maser is most likely present before an observable UC H  ii region is formed around a massive star and is quickly destroyed as the UC H  ii region evolves. There are 36 out of 97 maser sites that are linearly extended. The hypothesis that the maser emission is found in a circumstellar disc is not inconsistent with these 36 maser sites, but is unlikely. It cannot, however, account for all other maser sites. An alternative model which uses shocks to create the masing spots can more readily reproduce the maser spot distributions.     

Search for HH-objects and emission stars in star formation regions. VI. Herbig-Haro objects and emission stars in the region of the GM 1-64 and GM 2-4 nebulae

Three new Herbig-Haro and 12 emission stars, mainly belonging to the T Tau class, have been discovered in a study of the region of the GM 1-64 and GM 2-4 nebulae in the direction of the galactic anticenter. GM 1-64 and GM 2-4 are typical cometary nebulae illuminated by emission stars. In GM 2-4 the central star is surrounded by a dense dust envelope and is observed only in the IR. Two stellar-like sources which are bright in the IR are found in this same region and can be regarded as young, Class 1 stars. One of them (CPM 19) is surrounded by a compact group of fainter PMS objects. It is found that CPM 19 shows up clearly in the optical range and undergoes large amplitude brightness variations.     

Characteristics of infrared point sources associated with OH masers

We collect 3249 OH maser sources from the literature published up to April 2007, and compile a new catalog of OH masers. We look for the exciting sources of these masers and their infrared properties from IRAS and MSX data, and make a statistical study. MSX sources associated with stellar 1612 MHz OH masers are located mainly above the blackbody line; this is caused by the dust absorption of stellar envelopes, especially in the MSX A band. The mid-IR sources associated with stellar OH masers are concentrate...     

Optical identification of iras point sources based on low-dispersion fbs spectra. stars. iii

A third list of point sources from the IRAS Point Source Catalog (PSC), optically identified with late-type stars, is given. The list contains data on 34 objects. The identification was based on the Digitized Sky Survey (DSS), the First Byurakan Survey (FBS). blue and red maps of the Palomar Observatory Sky Survey, and infrared fluxes at wavelengths of 12, 25, 60, and 100 mm in the regions of +61° ≤ δ ≤ +65°, 06^h45^m ≤ α ≤ 17^h28^m and +69° ≤ δ ≤ +73°, 03^h50^m ≤ α ≤ 18^h10^m. Of 34 objects given in the IRAS PSC as unidentified sources of infrared radiation, 11 are associated with known stars in existing catalogs, 6 are objects from the FBS survey of late-type stars, and 17 sources remained unknown in the optical range, 3 of them also being sources in the IRAS Serendipitous Survey Catalog (SSC). The optical coordinates, their departures from the 1R coordinates, the V magnitudes, the color indices CI, and the preliminary spectral subtypes were determined. The objects have optical magnitudes in the range of 7^h.6-13^m.6. Finder charts from the DSS are given for 23 objects. Translated from Astrofizika, Vol. 43, No. 1, pp. 77-84, January–March, 2000.     

Positions of hydroxyl masers at 1665 and 1667 MHz

The Australia Telescope Compact Array has been used to observe more than 200 1665-MHz hydroxyl masers south of declination −16° and derive their positions with typical rms uncertainties of 0.4 arcsec. Many of the 1665-MHz maser sites are found to have 1667-MHz OH maser counterparts which are coincident, within the errors.
The resulting position list presented here includes all well-documented, previously reported 1665-MHz masers close to the Galactic plane in the galactic longitude range 230° (through 360°) to 13°. Nearly 50 newly discovered masers are also listed, chiefly in the longitude range 312° to 356°, where the observations were conducted as an intensive survey of a continuous zone close to the Galactic plane.
Many of the maser sites are discussed briefly so as to draw attention to those possessing properties that are unusual among this large sample. Most of the masers are of the variety found in star-forming regions – at the sites of newly formed massive stars and their associated ultracompact H ii regions. The new, accurate, positions reveal coincidences of the OH masers with the continuum radio emission, with the infrared emission from dust that accompanies such regions, and with emission from other maser species such as methanol at 6668 MHz and water at 22 GHz.
By-products of the survey, also presented here, include measurements of at least 11 objects that are not associated with massive star-forming regions. They comprise several OH/IR stars (detected at the 1667- or 1665-MHz transition of OH, though commonly found to be most prominent at the 1612-MHz transition) and several unusual masers that may pinpoint other varieties of late-type stars or protoplanetary nebulae.     

Pulsar Wind Nebulae in Egret Error Boxes

A remarkable number of pulsar wind nebulae (PWN) are coincident with EGRET γ-ray sources. X-ray and radio imaging studies of unidentified EGRET sources have resulted in the discovery of at least six new pulsar wind nebulae (PWN). Stationary PWN (SPWN) appear to be associated with steady EGRET sources with hard spectra, typical for γ-ray pulsars. Their toroidal morphologies can help determine the geometry of the pulsar which is useful for constraining models of pulsed γ-ray emission. Rapidly moving PWN (RPWN) with more cometary morphologies seem to be associated with variable EGRET sources in regions where the ambient medium is dense compared to what is typical for the ISM.     

Near-infrared imaging of the environment of 6.7-GHz methanol masers

Near-infrared (NIR) images at I , J , H and K bands were made of 12 southern 6.7-GHz methanol maser sources. Astrometry accurate to 0.5 arcsec was obtained. The positions of known H  ii regions, water masers, hydroxyl masers, and mid- and far-infrared objects in the region are examined in order to try to determine the nature of the methanol maser source. Deeply embedded NIR sources were found close to seven out of 14 maser sites. In three cases, no NIR source, H  ii region, water maser or hydroxyl maser could be found in likely association with the methanol masers.     

On the nature of the FBS blue stellar objects and the completeness of the Bright Quasar Survey

The second part of the First Byurakan Survey is aimed at detecting all bright (B < 16.5) UV-excess starlike objects in a large area of the sky. By comparison with other major surveys such as the ROSA T All Sky Survey, the ROSAT WGACAT catalogue of point sources, the IRAS survey, the 6cm Green Bank, the 1.4GHz NRAO VLA, and the 92cm Westerbork Northern sky surveys and with the catalogue of mean UBVdata on stars, we estimate the number of AGNs present in the FBS survey and its completeness. We have made spectroscopic observations of nine of the most promising FBS candidates. We have found six new QSOs, bringing the total number of known QSOs in this survey to 42. By comparison with the Bright Quasar Survey, we found that the completeness of this last survey is of the order of 70% rather than 30–50% as suggested by several authors. Based party on observations collected at the Observatorie de Haute-Provence (CNRS, France). The APS databases are supported by the National Foundation, the National Aeronautics and Space Administration, and the University of Minnesota, and are available at hup:// aps.umn.edu. The Digitized Sky Survey was produced at the Space Telescope Science Institute (STScI) under U.S. Government Grant NAG W-2166. Published in Astrofizika, Vol. 42, No. 1, pp. 5–22, January–March, 1999.     

Enhanced luminosity of young stellar objects in cometary globules

In this study we investigated the effects of external trigger on the characteristics of young stellar objects (YSOs) associated with cometary globules (CGs). We made optical spectroscopy of stars associated with star-forming CGs. We find that the masses of the most massive stars associated with CGs are correlated with the masses of the parent cloud but they are systematically larger than expected for clouds of similar mass from the relation M _max-star=0.33M _cl ^0.43 given by Larson (Mon. Not. R. Astron. Soc. 200:159, 1982). We have also estimated the luminosities of the IRAS sources found associated with CGs as a function of cloud mass and then compared them with those of the IRAS sources found associated with isolated opacity class 6 clouds (isolated and relatively away from large star forming regions). We find that the luminosities of IRAS sources associated with CGs are larger than those of the opacity class 6 clouds. These findings support results from recent simulations in which it was shown that the Radiation Driven Implosion (RDI) process, believed to be responsible for the cometary morphology and star formation, can increase the luminosity 1–2 orders of magnitudes higher than those of protostars formed without external triggering due to an increase in accretion rates. Thus implying that the massive stars can have profound influence on the star formation in clouds located in their vicinity.