scholarly journals Faint optical spiral tracers

1979 ◽  
Vol 84 ◽  
pp. 99-99
Author(s):  
Juan C. Muzzio
Keyword(s):  
Emission Line ◽  
Milky Way ◽  
Be Stars ◽  
Schmidt Telescope ◽  
Ob Stars ◽  
The Past ◽  
Hα Emission ◽  
Photographic Emulsions

The use of modern photographic emulsions and techniques allows for the discovery of optical spiral tracers much fainter than was possible in the past. Our searches for such faint objects deal with the Puppis, Vela, Crux, Circinus, Norma and Ara regions of the Milky Way using Kodak plates (baked in dry nitrogen) obtained with the Curtis Schmidt-telescope at Cerro Tololo Inter-American Observatory. We have discovered OB stars as faint as 15 mag on IIIa-J plates obtained with the thin prism, and Hα emission-line objects (many of which are Be stars) as faint as 16 mag on 127-04 plates obtained with the 4° prism.

scholarly journals Hα emission-line stars in molecular clouds

2019 ◽  
Vol 630 ◽  
pp. A90 ◽  
Author(s):  
Bertil Pettersson ◽  
Bo Reipurth
Keyword(s):  
Molecular Clouds ◽  
Young Stellar Objects ◽  
Be Stars ◽  
Stellar Objects ◽  
Strong Concentration ◽  
Ob Stars ◽  
Star Forming ◽  
Hα Emission ◽  
Objective Prism ◽  
Emission Stars

A deep objective-prism survey for Hα emission stars towards the Canis Major star-forming clouds was performed. A total of 398 Hα emitters were detected, 353 of which are new detections. There is a strong concentration of these Hα emitters towards the molecular clouds surrounding the CMa OB1 association, and it is likely that these stars are young stellar objects recently born in the clouds. An additional population of Hα emitters is scattered all across the region, and probably includes unrelated foreground dMe stars and background Be stars. About 90% of the Hα emitters are detected by WISE, of which 75% was detected with usable photometry. When plotted in a WISE colour–colour diagram it appears that the majority are Class II YSOs. Coordinates and finding charts are provided for all the new stars, and coordinates for all the detections. We searched the Gaia-DR2 catalogue and from 334 Hα emission stars with useful parallaxes, we selected a subset of 98 stars that have parallax errors of less than 20% and nominal distances in the interval 1050 to 1350 pc that surrounds a strong peak at 1185 pc in the distance distribution. Similarly, Gaia distances were obtained for 51 OB-stars located towards Canis Major and selected with the same parallax errors as the Hα stars. We find a median distance for the OB stars of 1182 pc, in excellent correspondence with the distance from the Hα stars. Two known runaway stars are confirmed as members of the association. Finally, two new Herbig-Haro objects are identified.

scholarly journals Simultaneous Spectroscopy and Polarimetry of Be Stars

1987 ◽  
Vol 92 ◽  
pp. 84-86
Author(s):  
D. R. Gies ◽  
David McDavid
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
Absorption Line ◽  
Line Profile ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Line Profiles ◽  
Initial Attempt ◽  
Rapid Variability ◽  
Hα Emission

Evidence is now accumulating that many Be stars display photospheric line profile variations on timescales of days or less that are probably caused by nonradial pulsations (Baade 1984; Penrod 1986). In some circumstances these pulsations can promote mass loss into the circumstellar envelope, and consequently the conditions in the inner part of the envelope may vary on similar timescales. Changes in the envelope could produce variations in the polarization and emission line profiles, and observers have reported rapid variability in both. We describe here an initial attempt to search for simultaneous variations in continuum polarization, Hα emission, and the He I λ6678 photospheric absorption line in order to investigate correlated changes on short timescales.

scholarly journals A new survey for Hα-emission-line stars and related objects in the SMC

1991 ◽  
Vol 148 ◽  
pp. 196-197 ◽  
Author(s):  
M. Meyssonnier ◽  
M. Azzopardi
Keyword(s):  
Emission Line ◽  
Magellanic Cloud ◽  
Small Magellanic Cloud ◽  
Schmidt Telescope ◽  
Hα Emission

New identifications of the Hα-emission-line objects in the Small Magellanic Cloud (SMC) have been made with the Curtis Schmidt telescope at Cerro Tololo Inter-American Observatory (CTIO).

scholarly journals Radio Stars of the SKA

Universe ◽  
2021 ◽  
Vol 7 (5) ◽  
pp. 119
Author(s):  
Bin Yu ◽  
Albert Zijlstra ◽  
Biwei Jiang
Keyword(s):  
Radio Emission ◽  
Milky Way ◽  
Galactic Plane ◽  
High Sensitivity ◽  
Hii Regions ◽  
Be Stars ◽  
M Dwarfs ◽  
Ob Stars ◽  
5 Ghz ◽  
Radio Stars

Radio emission from stars can be used, for example, to study ionized winds or stellar flares. The radio emission is faint and studies have been limited to few objects. The Square Kilometer Array (SKA) brings a survey ability to the topic of radio stars. In this paper we investigate what the SKA can detect, and what sensitivity will be required for deep surveys of the stellar Milky Way. We focus on the radio emission from OB stars, Be stars, flares from M dwarfs, and Ultra Compact HII regions. The stellar distribution in the Milky Way is simulated using the Besançon model, and various relations are used to predict their radio flux. We find that the full SKA will easily detect all UltraCompact HII regions. At the limit of 10 nJy at 5 GHz, the SKA can detect 1500 Be stars and 50 OB stars per square degree, out to several kpc. It can also detect flares from 4500 M dwarfs per square degree. At 100 nJy, the numbers become about 8 times smaller. SKA surveys of the Galactic plane should be designed for high sensitivity. Deep imaging should consider the significant number of faint flares in the field, even outside the plane of the Milky Way.

scholarly journals Variability of Some Be Stars on High-Resolution, High S/N Spectra

1988 ◽  
Vol 132 ◽  
pp. 131-134
Author(s):  
A. M. Hubert ◽  
H. Hubert ◽  
B. Dagostinoz ◽  
M. Floquet
Keyword(s):  
Emission Line ◽  
Time Scale ◽  
Signal To Noise Ratio ◽  
Complex Structure ◽  
Ccd Camera ◽  
Brightness Distribution ◽  
Short Time Scale ◽  
Be Stars ◽  
Rapid Variability ◽  
Hα Emission

Rapid variability in Be stars could be understood by non radial pulsations or by rotation of an inhomogeous surface brightness distribution…The structure and the variability of the Hα and of the HeI λ6678 lines have been investigated with an optical fiber spectrograph and a CCD camera. The signal to noise ratio, measured in the continuum, is between 300 and 500.Weak changes in the Hα emission line profile of γ Cas have been detected on time-scale of hours and days. This line has an asymmetric profile exhibiting only one blue-shifted maximum while the HeI λ6678 has a double-peak emission, superimposed to the photospheric contribution, with a violet to red peak ratio V/R >1.The Hα emission line of φ Per exhibits a complex structure with significant changes in its core, from night to night and on a short time scale <lhr. The HeI λ6678 presents a blue-shifted asymmetric emission (red-winged) superimposed to the photospheric contribution.Furthermore the Hel photospheric line λ6678 of the B6 star o And has presented notable variations in its profile during the 2 observational campaigns, which do not seem correlated to the photometric period of 1.57 day.

scholarly journals Confirmation of a Moving Component in the Hα Emission Line of LS I+61°303

2000 ◽  
Vol 175 ◽  
pp. 731-734
Author(s):  
Radoslav K. Zamanov ◽  
Josep Martí
Keyword(s):  
Radial Velocity ◽  
Emission Line ◽  
Spectral Feature ◽  
Outer Edge ◽  
The Past ◽  
Hα Emission

AbstractWe report our attempts to detect and confirm a narrow moving component in the Hα emission line of LS I+61°303. The existence of this spectral feature was already suspected in the past. As a result, we find that this component does exist and that its radial velocity varies in agreement with the radio period of the system. We interpret it tentatively as due to a denser region, or bulge, orbiting near the outer edge of the Hα emitting disk.

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

1995 ◽  
Vol 148 ◽  
pp. 388-394
Author(s):  
Bambang Hidayat ◽  
Katsuo Ogura ◽  
Masao Shinohara
Keyword(s):  
Emission Line ◽  
Planetary Nebulae ◽  
T Tauri Stars ◽  
Schmidt Telescope ◽  
Dark Clouds ◽  
T Tauri ◽  
Hα Emission ◽  
Objective Prism ◽  
Emission Stars

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.

scholarly journals Rapid variability of Hα emission line in Be stars

1994 ◽  
Vol 162 ◽  
pp. 254-256
Author(s):  
B. G. Anandarao ◽  
A. Chakraborty ◽  
R. Swaminathan ◽  
B. Lokanadham
Keyword(s):  
Emission Line ◽  
Emission Lines ◽  
Be Stars ◽  
Rapid Variability ◽  
Fabry Perot ◽  
Dark Counts ◽  
Hα Emission

We have initiated an observational campaign on some bright Be stars in order to investigate the rapid variability in emission lines using a Fabry-Perot spectrometer(λ/δλ = 104; FSR = 21.3Å) at the Nasmyth focus of the 1.22 m JRO telescope at Hyderabad, India. The PMT dark counts were 1 – 2sec-1. Here we report our first observations on four stars.

scholarly journals Evolution and appearance of Be stars in SMC clusters

2009 ◽  
Vol 5 (S266) ◽  
pp. 470-473
Author(s):  
C. Martayan ◽  
D. Baade ◽  
Y. Frémat ◽  
J. Zorec
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Open Cluster ◽  
Central Star ◽  
Open Clusters ◽  
Be Stars ◽  
Ob Stars ◽  
Be Star ◽  
The Impact ◽  
Key Parameter

AbstractStar clusters are privileged laboratories for studying the evolution of massive stars (OB stars). One particularly interesting question concerns the phases during which the classical Be stars occur, which—unlike HAe/Be stars—are not pre-main-sequence objects, nor supergiants. Rather, they are extremely rapidly rotating B-type stars with a circumstellar decretion disk formed by episodic ejections of matter from the central star. To study the impact of mass, metallicity, and age on the Be phase, we observed Small Magellanic Cloud (SMC) open clusters with two different techniques: (i) with the ESO–WFI in slitless mode, which allowed us to find the brighter Be and other emission-line stars in 84 SMC open clusters, and (ii) with the VLT–FLAMES multifiber spectrograph to determine accurately the evolutionary phases of Be stars in the Be-star-rich SMC open cluster NGC 330. Based on a comparison to the Milky Way, a model of Be stellar evolution, appearance as a function of metallicity and mass, and spectral type is developed, involving the fractional critical rotation rate as a key parameter.

The Long View of Planetary Systems

2018 ◽  
Author(s):  
Karel Schrijver
Keyword(s):  
Solar System ◽  
Milky Way ◽  
Planetary Systems ◽  
Giant Planets ◽  
Milky Way Galaxy ◽  
Population Statistics ◽  
The Past ◽  
General Terms ◽  
The Galaxy ◽  
The Universe

How many planetary systems formed before our’s did, and how many will form after? How old is the average exoplanet in the Galaxy? When did the earliest planets start forming? How different are the ages of terrestrial and giant planets? And, ultimately, what will the fate be of our Solar System, of the Milky Way Galaxy, and of the Universe around us? We cannot know the fate of individual exoplanets with great certainty, but based on population statistics this chapter sketches the past, present, and future of exoworlds and of our Earth in general terms.

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