Emission Stars Research Articles

Some Results of an Hα Survey in the Taurus Dark Clouds

AbstractFrom a series of 4° objective-prism plates obtained on the 1 m Schmidt telescope of the Byurakan Astrophysical Observatory, 20 new Hα emission line stars were found. The intensity of Hα emission line was evaluated for these stars. An additional sample of probable Hα emission stars was also found. We present here details and some observational features of these stars. The total number of Hα emission line stars estimated for the surveyed area is about 80.

The Young Massive Stellar Objects of M17

We present a multiwavelength spectroscopic survey that reveals the ionizing cluster of M17 and uncovers a population of young stellar objects (YSOs) of high mass (M similar to 5-20 M.). The masses of the stars have been determined fairly accurately through optical or near-infrared spectral classification. We find strong circumstantial evidence for disks around the massive YSOs in the following forms: near-infrared excess, optical veiling, CO band-head emission, and/or Pa delta emission. We find a direct correlation between those YSOs that show CO band-head emission at 2.3 mu m and these stars in our survey that show Pa delta emission; in three of the four Pa delta emission stars this line is double peaked (suggestive of a bipolar wind or a rotating disk or envelope). Our data suggest that circumstellar material, possibly in the form of a disk, is prevalent among very young objects of fairly high mass. Based on considerations of disk lifetimes in other young clusters, the M17 cluster appears to be very young, perhaps less than 1 Myr.We have also identified at least nine O stars and a couple of late-O/early-B stars, most behind more than 8 mag of visible extinction using either optical or near-infrared spectral types. Several stars have inferred masses in excess of 60 M., and they look to be very close to the predicted zero-age main sequence with an estimated age of about 1 Myr, consistent with the age of the massive YSOs in the cluster. We have used the O stars to determine the distance to M17, which assumes the stars to lie on the zero-age main sequence (1300(-200)(+400) pc). While we attempt to determine an initial mass function for the cluster, it is incomplete even at high masses because of regions of extremely high extinction (A(V) > 20) in the cluster. We have also used the M17 O stars to study the dust properties in the local cloud and the behavior of the diffuse interstellar bands (DIBs) along this sight line, over the extinction range of A(V) = 3-10. The DIBs over this extinction range show little change in spectral shape nor a significant increase in strength. We suggest the features are already saturated at small A(V), or the material local to M17, where the increased extinction is being traced, does not contain the carriers of the DIB feature.

New 115-1115-1115-1objects in dark nebulae. II.

Results of a search for new emission objects in the region of dark nebulae are presented. The observations were made in 1979 and 1985 at the 40″ Schmidt telescope of the Byurakan Astrophysical Observatory. The spectra were obtained with a 4° objective prism (∼1100A/mm near Hσ) on Kodak 103aE, 103aF, IIaF, and IIIaF plates with the use of RG1 and RG2 filters. Of the 52 emission stars discovered, five show variability in the Hσ line intensity.

New Hα objects in dark nebulae. I.

Results of a search for new Hα objects in the Cepheus region are presented. The observations on which the search was based were made in 1979 and 1985 at the 40″ Schmidt telescope of the Byurakan Astrophysical Observatory with a 4° objective prism. Of the 80 emission stars detected, 68 are new. Most of them are fainter than the sun in absolute magnitude. A large fraction of the emission stars discovered may be flare stars as well as T Tau and Herbig Ae/Be stars.

Trapezium systems containing T tauri stars

The results of a spectroscopic investigation of four stars comprising a Trapezium system in the nebula Sh 155 are presented. The stars have a number of emission lines typical of red emission stars and T Tau stars. This system is one of the 13 systems which we have found in the Palomar atlas. It is shown that all of these systems are members of OB associations.

A Very Active T Tauri Star in NGC 7129

The star forming region NGC 7129 was first studied by Herbig (1960), who discovered two bright (BD+65° 1637 and LkHα234) and some weaker Hα emission stars. Subsequent investigations in this region led to the detection of five Herbig-Haro objects (Strom et al. 1974, Gyulbudaghian et al. 1978, Eiroa et al. 1992) and one T Tauri star, V350 Cep (Gyulbudaghian & Sarkissian 1977). Some non-stable stars in NGC 7129 are surrounded by reflection and cometary nebulae.Our Hα-emission survey (Semkov &: Tsvetkov 1986) revealed an interesting irregular variable star in the dark clouds near the emission nebulae. On objective prism plates the star shows very strong Hα-emission and was included in our list of such stars as No. 7. An identification chart and the coordinates can be found in Semkov (1993a). The observations reported here include long-time photographic photometry and CCD spectroscopic and photometric observations.

A Large Number of Herbig-Haro Candidates Found by the Contrast Enhancement and Unsharp Masking Technique

AbstractAbout 1300, 60 and 70 Herbig-Haro candidates have been picked up in the Ori A/L1641, Ori B/L1630 and NGC 2264/Mon OBI regions, respectively, on deep Schmidt plates. The contrast enhancement and unsharp masking technique has been applied simultaneously. Unsharp masking applied to an objective-prism Schmidt plate for the Carina Nebula region has yielded the detection of 38 Hα emission stars, of which 13 are new findings.

Emission-Line Stars in the Outer Part of the Orion Star-Forming Region

In a series of emission-line star survey programs we have conducted wide and deep survey observations for Hα emission stars in the Orion star-forming region. The first result for the Kiso area A-0904 (5°x5°, centered at α = 5h40m and δ = +0°) was presented in Paper I (Wiramihardja et al., 1989), followed by Paper II (Kogure et al., 1989) for the area A-0903 (α = 5h20m, δ = −5° and A-0976 (α = 5h40m, δ = −5°). In Paper IV the results for the areas A-1047 (α = 5h20m, δ = −10° and A-1048 (α = 5h40m, δ = −10°) are given.

Wolf-Rayet and OF stars in the OB associations LH 101 and LH 104 in the LMC

We observed in the Large Magellanic Cloud the associations LH 101 and LH 104, containing six Wolf-Rayet stars: one WN and five WCE subtypes. These regions are located south of the 30 Dor nebula. The new observations include UBV photometry for a thousand stars and spectroscopy in the range from 3600 to 5300 Å for about 90 stars. In LH 101 an 06.5f, an 06.5 + WN8 and a hydrogen emission star are identified. Cluster HR diagrams of these OB associations reveal their age structure.

Surveys for Hα Emission-Line Stars using the Bosscha Schmidt Telescope

According to McCarthy (1984) the objects detected in objective prism surveys for Hα emission line are a ”most unnatural“ group. Of course they consist of many natural groupings whose identities or other peculiarities could become apparent after observing them with higher dispersion and resolution spectroscopy. In some cases, however, their galactic locations and associations with other known populations, can provide a clue to their population types.The aims of the objective prism surveys using the Bosscha Schmidt telescope can be broadly categorised as follows: 1.Searches for galactic planetary nebulae in the region 240° < l < 360 °; |b| ≤ 10°, initiated by The (1968).2.Searches for T-Tauri stars in some southern dark clouds (Shinohara, Ogura & Hidayat 1989).3.Searches for variations in Hα intensities and luminous emission stars in some selected galactic regions, such as in the Puppis and Carina regions.

H emission stars in the Circinus region

Hα emission objects were searched for, using objective-prism Schmidt plates in a 5 deg2 sky area around the Circinus R2 region. 47 emission stars have been detected, 45 of which are new findings. Low-dispersion slit spectroscopy was obtained for some of them, and objective-prism Schmidt observations in the blue–violet region were used in order to clarify their nature. These observational data, together with the properties of the IRAS sources associated with some of them, indicate that the detected emission stars are mostly T Tauri stars or related objects. They make two spatially distinct groups, one located in a dark cloud complex including D316.9 – 3.8 and the other near the north-eastern margin of D318.2 – 4.3C. We propose to designate them as Cir T1 and T2 associations, respectively.

The stellar population of the Lupus clouds

view Abstract Citations (177) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Stellar Population of the Lupus Clouds Hughes, Joanne ; Hartigan, Patrick ; Krautter, Joachim ; Kelemen, Janos Abstract We present photometric and spectroscopic observations of the H alpha emission stars in the Lupus dark cloud complex. We estimate the effective temperatures of the stars from their spectral types and calculate the reddening towards each object from the (R-I) colors. From these data, we derive mass and age distributions for the Lupus stars using a new set of pre-main sequence evolutionar tracks. We compare the results for the Lupus stars with those for a similar population of young stellar objects in Taurus-Auriga and Chamaeleon and with the initial mass function for field stars in the solar neighborhood. From the H-R diagrams, Lupus appears to contain older stars than Taurus. The Lupus dark clouds form a greater proportion of low mass stars than the Taurus complex. Also, the proportion of low mass stars in Lupus is higher than that predicted by the Miller-Scalo initial mass function, and the lowest mass stars in Lupus are less active than similar T Tauri stars in other regions. Publication: The Astronomical Journal Pub Date: September 1994 DOI: 10.1086/117135 Bibcode: 1994AJ....108.1071H Keywords: Molecular Clouds; Star Formation; Stellar Mass; Stellar Physics; Stellar Spectra; T Tauri Stars; Astronomical Photometry; Astronomical Spectroscopy; Chronology; Graphs (Charts); Populations; Spectral Emission; Spectral Energy Distribution; Spectrum Analysis; Tables (Data); Astronomy; STARS: PRE-MAIN SEQUENCE full text sources ADS | data products SIMBAD (78)

THE PECULIAR NATURE OF BD +24 676

ABSTRACT The H-alpha emission star BD +24 676, formerly classified as a T Tauri star and more recently as a Herbig Ae star, has been observed at moderately high resolution in the red spectral region. The main results are: the metallic lines over the wavelength range 6400-6750 angstroms have equivalent widths comparable to early G stars; the radial velocity is not consistent with that of members of Tauris-Auriga; the lithium abundance is much lower than expected for a T Tauri star; H-alpha has a changing complex profile. The data do not appear to be compatible with the hypothesis that BD +24 676 is a pre-main sequence star. The properties can be qualitatively understood if it is a close binary composed by a cool post-main sequence subgiant and a hot main-sequence star, although more data are needed to clarify its nature.

H-alpha and broadband photometric monitoring of ten M dwarfs - Flares and spots

A set of ten dM3/dM4 stars with a wide range of H-{alpha} equivalent widths, W(H-{alpha}), including both dM and dMe stars, has been monitored in U, V, and H-{alpha}. The time resolution of the data is 3-5 min. A strong correlation is found between the minimum or 'quiescent' value of W(H-{alpha}) for each star and its degree of variability in H-{alpha}. The emission stars in this sample varied by about a factor of 2 in W (H-{alpha}) during flares. A weak correlation also exists between quiescent H-{alpha} and the degree of variability in V. This is caused both by flare contamination of the V bandpass and by the presence of cool spots on at least one of the program stars, Gl 873. Nineteen flare events were detected on the four strongest emission line stars in the sample. To within the crude time resolution of this study, most flares were coincident in U and W(H-{alpha}). However, the largest flare (on Gl 896) clearly showed a lag of at least 20 min between the peak in U and the peak in H-alpha, and the second largest flare showed a similar lag of perhaps 10 min. 17 refs.

A Wide and Deep Survey of Emission-line Stars in the Orion Region

AbstractWe have carried out an extensive survey of Hα emission stars in the Orion region over an area of about 100 deg2. We present the results for the areas A-0975 and A-0976 of about 25 deg2 each.

Auvby? survey for Ca II emission stars

During the last two years auvbyβ photometric survey of 85 Ca II emission stars from the Mount Wilson program on stellar activity has been carried out at the Calar Alto Observatory (Almeria, Spain). We present preliminary results for theuvby and β calibrations. Some stars displaying anomalousc1 andm1 indices, with photometric or spectroscopic data from previous studies, are reported. A reddening study for the complete sample is given.

NEW BRIGHT HYDROGEN EMISSION STARS III

ABSTRACT Three-hundred-sixteen bright early-type stars not known to exhibit hydrogen emission have been observed at H-alpha. Ten new emission stars have been found. One of the stars, HD 147196, is a probable member of the upper Scorpius association.

Solar-type stars in Cepheus OB 2: H? emission stars and IRAS point sources

A survey for emission line stars was carried out in 1980 with the Schmidt telescope of Konkoly Observatory in the region of IC 1396 (Kun, 1986a, hereafter referred to as Paper I). This work was aimed at a preliminary mapping of the probable medium mass members of the association Cepheus OB 2. The stars of the region have been followed since then with the same telescope in order to obtain a more complete view on the stellar content of this giant star-forming region. The common variability of the Hα emission strength makes the sense of repeating such surveys. The new survey resulted in the discovery of 65 further emission stars. Equatorial coordinates and finding charts are given for them.

Surface distribution of the luminous and early‐type emission stars in the OB Vulpecula associations

AbstractThe surface distribution of the luminous and early‐type emission stars in a Milky Way region in Vulpecula is obtained. The results show a discrepancy between the places of greatest concentration of such kinds of stars and those indicated in literature as positions of OB associations.

IRAS Infrared Fluxes of RV Tauri Stars

Data resulting from the IRAS survey relating to the stars of the RV Tauri class have been examined. Of a total of 78 objects definitely assigned to this class in the 4th edition of the GCVS, 33 are to be found in the Point-Source Catalogue, and for six of these spectral data are available in the low-resolution Spectral Atlas (to 22.6 μm published by the IRAS Science Team (A & A Suppl. 65, 607, 1986). In the latter the pronounced difference in infrared emission between the carbon-rich star AC Her and most other RV Tauri stars, first noted by Gehrz in 1972, is striking, taking the form of a very marked continuation of that star's emission to at least 22 μm.