scholarly journals Identification of new Classical Ae stars in the Galaxy using LAMOST DR5

2020 ◽  
Author(s):  
R Anusha ◽  
Blesson Mathew ◽  
B Shridharan ◽  
R Arun ◽  
S Nidhi ◽  
...  
Keyword(s):  
Spectral Type ◽  
Far Infrared ◽  
Emission Lines ◽  
Be Stars ◽  
Infrared Excess ◽  
Star Catalog ◽  
Rotation Rates ◽  
The Galaxy ◽  
Evolutionary Phase ◽  
Optical Color

Abstract We report the first systematic study to identify and characterize a sample of classical Ae stars in the Galaxy. The spectra of these stars were retrieved from the A-star catalog using the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) survey. We identified the emission-line stars in this catalog from which 159 are confirmed as classical Ae stars. This increases the sample of known classical Ae stars by about nine times from the previously identified 21 stars. The evolutionary phase of classical Ae stars in this study is confirmed from the relatively small mid- and far-infrared excess and from their location in the optical color-magnitude diagram. We estimated the spectral type using MILES spectral templates and identified Classical Ae stars beyond A3, for the first time. The prominent emission lines in the spectra within the wavelength range 3700 – 9000 Å are identified and compared with the features present in classical Be stars. The Hα emission strength of the stars in our sample show a steady decrease from late-B type to Ae stars, suggesting that the disc size may be dependent on the spectral type. Interestingly, we noticed emission lines of Fe ii, O i and Paschen series in the spectrum of some classical Ae stars. These lines are supposed to fade out by late B-type and should not be present in Ae stars. Further studies, including spectra with better resolution, is needed to correlate these results with the rotation rates of classical Ae stars.

scholarly journals Interacting Binaries as Be Stars

1987 ◽  
Vol 92 ◽  
pp. 451-455
Author(s):  
Mirek J. Plavec
Keyword(s):  
Spectral Type ◽  
Binary Stars ◽  
Emission Lines ◽  
Close Binary ◽  
High Electron ◽  
Be Stars ◽  
Close Binary Stars ◽  
High Ionization ◽  
Mass Outflow ◽  
Balmer Lines

AbstractSemidetached close binary stars of the Algol type often have primary components of spectral type A0 or earlier and display emission at Hα (sometimes also at higher Balmer lines). They are therefore Be stars. Many binaries of this type are not eclipsing and must look like “ordinary” Be stars. We have discovered high-ionization emission lines of N V, C IV, Si IV, Fe III, etc. in the ultraviolet spectra of totally eclipsing Algols. They probably originate in circumstellar turbulent regions at fairly high electron temperatures, of the order of 100 000 K. They are not detectable in most non-eclipsing systems, but may be there and may play an important role in the dynamics of accretion and mass outflow from the systems.

scholarly journals 7.5. Tentative detection of far infrared excess in Arp 220

1998 ◽  
Vol 184 ◽  
pp. 301-302
Author(s):  
Kin-Wing Chan ◽  
S. H. Moseley ◽  
E. Dwek ◽  
T. L. Roellig ◽  
S. Casey ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Time Scale ◽  
Far Infrared ◽  
Infrared Emission ◽  
Short Time Scale ◽  
Active Nucleus ◽  
Infrared Excess ◽  
Grating Spectrometer ◽  
The Galaxy ◽  
Short Time

We report 36 to 50 μm observations of Arp 220 by the Goddard Cryogenic Grating Spectrometer on the Kuiper Airborne Observatory in May 1994. In this measurement, we find the galaxy to be four times brighter than in the measurements of Joy et al. (1986). If both of the observations are correct, this large far infrared luminosity increasing in a short time scale between the two observations suggests that the infrared emission in Arp 220 consists mostly of nonthermal synchrotron radiation which originates from the active nucleus.

scholarly journals Multiwavelength observations of the Be-star/X-ray binary EXO2030+375 during outburst

1994 ◽  
Vol 162 ◽  
pp. 206-207
Author(s):  
A.J. Norton ◽  
M.J. Coe ◽  
C. Everall ◽  
P. Roche ◽  
L. Bildsten ◽  
...  
Keyword(s):  
Neutron Star ◽  
Emission Lines ◽  
Be Stars ◽  
Infrared Excess ◽  
X Ray ◽  
Circumstellar Material ◽  
Spin Period ◽  
Be Star ◽  
Star Surface ◽  
X Ray Binaries

EXO2030+375 consists of a neutron star in an eccentric 46 day orbit around a 20th magnitude Be-star companion (Coe et al., 1988; Parmar et al., 1989; Stollberg et al., 1993). The Be-star is thought to be surrounded by a shell/disc of material which is responsible for the infrared excess and Balmer emission lines which are characteristic of Be-stars in general. At periastron, the neutron star passes through this circumstellar material, giving rise to enhanced accretion onto the neutron star surface. As a result of this, the X-ray emission (pulsed at the neutron star spin period of 41.8s) increases dramatically, so producing the transient, outburst behaviour which is commonly seen in Be-star / X-ray binaries.

scholarly journals Paschen Decrements in Be Stars

1976 ◽  
Vol 70 ◽  
pp. 227-227
Author(s):  
D. Briot
Keyword(s):  
Theoretical Calculations ◽  
Physical Characteristics ◽  
Emission Lines ◽  
Be Stars ◽  
Infrared Excess ◽  
General Properties

We searched for the general properties of the Be stars with Paschen emission lines. First, we obtained a relation between the infrared excess of the Be stars and the presence of emission in the Paschen lines. Until now, these emission excesses could be related to no physical characteristics of classical Be stars. Then, the measures of Paschen decrements of 12 stars whose spectral types range from B0e to B5e allowed us to check several theoretical calculations about the formation of emission lines in the envelopes of Be stars. Thus we can see the prominent part played by the electronic collisions in the Sobolev theory. Indeed, only with calculations taking the electronic collisions into account, can we obtain theoretical values agreeing with both measured Paschen and Balmer decrements for the hottest stars of our sample. However, no theoretical values agree with the observed decrements for the cooler stars.

scholarly journals On the formation of Balmer emission lines in the model envelopes of Be stars

1994 ◽  
Vol 162 ◽  
pp. 378-379
Author(s):  
T. Kogure ◽  
S. Suzuki ◽  
M. Mon
Keyword(s):  
Spectral Type ◽  
Emission Lines ◽  
Line Of Sight ◽  
Physical Parameters ◽  
Be Stars ◽  
Large Scatter ◽  
Stellar Radiation ◽  
Balmer Lines

We consider the formation of the Balmer emission lines and the decrement Hα/Hβ/Hγ, by solving the non-LTE problems in elementary regions of the envelope divided by equal line-of-sight velocities. These envelope-elements are characterized by different optical depths in the Balmer lines and by different dilution factors for the incident stellar radiation. It is shown that the decrements sensitively depend on these parameters of the envelope-elements. We show that the observed spectral-type dependence and large scatter of the decrements among Be stars can be explained in terms of the variation of these physical parameters.

scholarly journals Constraining the progenitor evolution of GW 150914

2018 ◽  
Vol 14 (S346) ◽  
pp. 444-448
Author(s):  
Jorick S. Vink
Keyword(s):  
Magellanic Clouds ◽  
Emission Lines ◽  
Stellar Winds ◽  
Stellar Rotation ◽  
Rotation Rates ◽  
Polarised Light ◽  
The Galaxy ◽  
Low Metallicity ◽  
Initial Results ◽  
Promising Avenue

AbstractOne of the largest surprises from the LIGO results regarding the first gravitational wave detection (GW 150914) was the fact the black holes (BHs) were “heavy”, of order 30 - 40 Mȯ. The most promising explanation for this obesity is that the BH-BH merger occurred at low metallicity (Z): when the iron (Fe) contents is lower this is expected to result in weaker mass loss during the Wolf-Rayet (WR) phase. We therefore critically evaluate the claims for the reasons of heavy BHs as a function of Z in the literature. Furthermore, weaker stellar winds might lead to more rapid stellar rotation, allowing WR and BH progenitor evolution in a chemically homogeneous manner. However, there is as yet no empirical evidence for more rapid rotation amongst WR stars in the low Z environment of the Magellanic Clouds. Due to the intrinsic challenge of determining WR rotation rates from emission lines, the most promising avenue to constrain rotation-rate distributions amongst various WR subgroups is through the utilisation of their emission lines in polarised light. We thus provide an overview of linear spectro-polarimetry observations of both single and binary WRs in the Galaxy, as well as the Large and Small Magellanic Clouds, at 50% and 20% of solar Z, respectively. Initial results suggest that the route of chemically homogeneous evolution (CHE) through stellar rotation is challenging, whilst the alternative of a post-LBV or common envelope evolution is more likely.

scholarly journals Infrared observations of GGD objects

1987 ◽  
Vol 122 ◽  
pp. 125-126
Author(s):  
R. Carballo ◽  
C. Eiroa ◽  
A. Mampaso
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Far Infrared ◽  
Infrared Emission ◽  
Be Stars ◽  
Main Sequence Stars ◽  
Infrared Excess ◽  
Dark Clouds ◽  
Infrared Sources ◽  
Different Characteristics

We present accurate positions and near infrared photometry (Table I) of 11 point-like objects in the neighbourhood of GGD objects obtained on the 1.55 m and on the 1.23 m in Teide Obs. and Calar Alto Obs. respectively, in Spain. Several of the near infrared sources are directly associated with the GGD nebulae and/or are candidate for their excitation. In addition some of them seem to be the near infrared counterparts of IRAS sources. We believe, on the basis of their infrared excess, far infrared emission (IRAS), association with nebulosity, coincidence with H2O masers or the fact that in most cases the observed luminosities are higher than those expected for main sequence stars, that most of them (9/12) are young stars embedded in the dark clouds which contain the GGD objects. The loci of the detected sources in an (H-K,K-L) infrared two-colour diagram is the same as that obtained for known pre-main sequence stars, such as T Tauris and Herbig Ae-Be stars, indicating the presence of dust shells with temperatures in the range 800–1500 K. The observed range in luminosity, 10–4600 L⊙, added to other different characteristics found between them, such' as the presence, or absence, of H2O masers, indicates the interest for a detailed study of the infrared sources and related GGD nebulae.

scholarly journals Dust formation of Be stars with large infrared excess

2010 ◽  
Vol 6 (S272) ◽  
pp. 366-371
Author(s):  
Chien-De Lee ◽  
Wen-Ping Chen
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Thermal Emission ◽  
Far Infrared ◽  
Dust Particles ◽  
Be Stars ◽  
Ionized Gas ◽  
Infrared Excess ◽  
Star Forming ◽  
Infrared Wavelengths

AbstractClassical Be stars, in addition to their emission-line spectra, are associated with infrared excess which is attributable to free-free emission from ionized gas. However, a few with exceptionally large near-infrared excess, namely with J–H, and H–Ks both greater than 0.6 mag—and excess emission extending to mid- and far-infrared wavelengths—must be accounted for by thermal emission from circumstellar dust. Evolved Be stars on the verge of turning off the main sequence may condense dust in their expanding cooling envelopes. The dust particles should be very small in size, hence reprocess starlight efficiently. This is in contrast to Herbig Ae/Be stars for which the copious infrared excess arises from relatively large grains as part of the surplus star-forming materials.

scholarly journals The Distribution of M Supergiants with Large Infrared Excess and WR Stars in the Galaxy

1991 ◽  
Vol 143 ◽  
pp. 641-642
Author(s):  
M. Raharto
Keyword(s):  
Spectral Type ◽  
The Other ◽  
Early Type ◽  
Infrared Excess ◽  
Giant Stars ◽  
Other Hand ◽  
The Galaxy ◽  
M Stars

From the m12 – m25vs. spectral type diagram (see for example: Habing, 1987, Figure 5), it can be seen that there are no early M giant stars with m12 – m25 > 0.7. On the other hand all early M stars with m12 – m25 > 0.7 are M supergiants. These early type M supergiants have typically infrared excesses at 12 μm in the range of 20 to 170 times higher than their photosperic fluxes.

scholarly journals Rotating Stellar Atmospheres (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 106-122
Author(s):  
Joseph P. Cassinelli
Keyword(s):  
Radiation Transfer ◽  
Review Paper ◽  
Theoretical Models ◽  
Stellar Atmospheres ◽  
Be Stars ◽  
Line Profiles ◽  
Intrinsic Polarization ◽  
Infrared Excess ◽  
Rotation Rates ◽  
Distribution Line

AbstractThe effects of rapid rotation on the emergent energy distribution, line profiles, atmospheric motions and polarization are discussed. A simplified explanation of some of the effects is presented. Results of detailed radiation transfer calculations are briefly reviewed. The rotation can lead to circulation and turbulent motions in the photospheric layers which could affect the outflow from the Be stars. The rotation rates actually observed in the Be stars are sufficiently below the critical rate that many of the effects predicted by the plane parallel atmosphere calculations should be small. Nevertheless, the models are useful and necessary for estimating rotation speeds from lines that are widely separated in wavelength. The rapidly rotating photospheric models predict far too small an infrared excess, as well as too small an intrinsic polarization. The explanation of these observations requires that geometrically extended envelopes be considered. Theoretical models for the intrinsic polarization are critically discussed. It is stressed that polarization is a powerful diagnostic for determining the asymmetrical structure of the outer atmospheres of the Be stars.

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