A multiband optical polarimetric study of classical Be stars with exceptionally large near-infrared excess

2013 ◽  
Author(s):  
Chien-De Lee ◽  
C. Eswaraiah ◽  
A. K. Pandey ◽  
Wen-Ping Chen
Keyword(s):  
Near Infrared ◽  
Be Stars ◽  
Infrared Excess ◽  
Polarimetric Study

scholarly journals Near-infrared excess and emission characteristics of classical Be stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 404-405
Author(s):  
Chien-De Lee ◽  
Wen-Ping Chen ◽  
Daisuke Kinoshita
Keyword(s):  
Emission Line ◽  
Near Infrared ◽  
Thermal Emission ◽  
Temporal Correlation ◽  
Circumstellar Dust ◽  
Emission Characteristics ◽  
Spectral Features ◽  
Be Stars ◽  
Infrared Excess ◽  
Fast Rotating

AbstractClassical Be (CBe) stars are fast-rotating emission-line stars associated with infrared excess often attributed to plasma free-free emission. A few with exceptionally large near-infrared excess, namely with (J–H) and (H–Ks) both greater than 0.6 mag, however, must be accounted for by thermal emission from circumstellar dust. From 2007 to 2009, spectra of more than 100 CBe stars have been collected. We present some of these spectra and discuss how temporal correlation (or lack of) among spectral features would provide possible diagnosis of the origin of the CBe phenomena.

scholarly journals Do Herbig Ae/Be Stars Have Disks?

1997 ◽  
Vol 163 ◽  
pp. 525-530 ◽  
Author(s):  
T.P. Ray ◽  
M. Corcoran
Keyword(s):  
Equivalent Width ◽  
Near Infrared ◽  
Mass Loss Rate ◽  
Line Emission ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Be Stars ◽  
Infrared Excess ◽  
T Tauri ◽  
Outflow Rate

AbstractThe Herbig Ae/Be stars are optically visible pre-main sequence stars of intermediate mass (M* ≈ 3−8M⊙) and are thought to be the higher mass analogues of the T Tauri stars. While there is no doubt that classical T Tauri stars, i.e. those with EW(Hα) ≳ 10 Å, are surrounded by disks, it remains controversial as to whether this is the case with the equivalent Herbig Ae/Be stars. It has even been questioned whether the powerful winds that are ejected by Herbig Ae/Be stars are driven by accretion. To address these problems we have examined a large sample of these stars with the idea of using their forbidden line emission as an indirect diagnostic for the presence of disks. Striking similarities with the classical T Tauri stars are found. For example we have discovered evidence not only for a strong correlation between near-infrared colours and the equivalent width of the forbidden line emission but also that the forbidden line emission normally arises in a blueshifted outflow component. It has already been shown in the case of the classical T Tauri stars that the correlation of near-infrared colour with forbidden line equivalent width is due to a link between the accretion rate and the outflow rate. The virtually identical relationship seen in the case of the Herbig Ae/Be stars must then also have a similar origin. Our finding that the forbidden line emission in Herbig Ae/Be stars is normally blueshifted shows not only that it arises in an outflow but, as in the classical T Tauri stars, such an asymmetry in the velocity centre of the line must be caused by the obscuring effects of a disk. We find that the correlation seen in the classical T Tauri stars between the mass-loss rate and infrared excess can be extended, when we include the Herbig Ae/Be stars, to cover almost 5 orders of magnitude in stellar luminosity. Our observations therefore broaden the findings of earlier observers for low mass young stars and indicate the presence of circumstellar disks around the majority of Herbig Ae/Be stars with forbidden line emission. A corollary of our results is that the same outflow mechanism must operate in both the classical T Tauri stars and the Herbig Ae/Be stars with forbidden line emission.

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 Polarimetry and Physics of Be Star Envelopes (Review paper)

1982 ◽  
Vol 98 ◽  
pp. 77-93 ◽  
Author(s):  
George V. Coyne ◽  
Ian S. McLean
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Theoretical Models ◽  
Geometrical Parameters ◽  
Be Stars ◽  
Intermediate Band ◽  
Wide Range ◽  
Recent Developments ◽  
Be Star ◽  
Polarization Studies

A review of the most recent developments in polarization studies of Be stars is presented. New polarization techniques for high-resolution spectropolarimetry and for near infrared polarimetry are described and a wide range of new observations are discussed. These include broadband, intermediate-band and multichannel observations of the continuum polarization of Be stars in the wavelenght interval 0.3–2.2 microns, high resolution (0.5 Å) line profile polarimetry of a few stars and surveys of many stars for the purposes of statistical analyses. The physical significance of the observational material is discussed in the light of recent theoretical models. Emphasis is placed on the physical and geometrical parameters of Be star envelopes which polarimetry helps to determine.

scholarly journals Multiple dust shells around Herbig Ae/Be stars

1987 ◽  
Vol 122 ◽  
pp. 99-100
Author(s):  
P.S. Thé ◽  
D. N. Dawanas
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Spectral Energy Distribution ◽  
Far Infrared ◽  
Central Star ◽  
Spectral Energy ◽  
Be Stars ◽  
Intermediate Mass ◽  
Dust Shells ◽  
Average Size

Intermediate mass (2 < M/M⊙ < 9) pre-main sequence objects, also named Herbig Ae/Be stars, are known to have excess radiation in the near-infrared. From IRAS o bservations it turns out without doubt (quality 3, high S/N radio), that these objects are very strong far-infrared emitters at 12, 25, 60 and often also at 100 μm. The spectral energy distribution, depicted in Fig. 1 for intermediate mass pre-main sequence stars, show clearly this large excess. From the difference curves it is apparent that this excess radiation is most probably caused by several dust shells. Using very simplified methods it is possible to derive the average temperature of the dust shells (see Thé, Wesselius, Tjin A Djie and Steenman, 1986). If the chemical composition of the mixture of the dust grains and their average size are assumed it is also possible to estimate other characteristics like the distance from the central star and the mass of the dust shells (see Thé, Hageman, Westerlund, Tjin A Djie, 1985).

scholarly journals The infrared view of dust and molecules around V4334 Sgr (Sakurai’s object): a 20-yr retrospective

2020 ◽  
Vol 493 (1) ◽  
pp. 1277-1291 ◽  
Author(s):  
A Evans ◽  
R D Gehrz ◽  
C E Woodward ◽  
D P K Banerjee ◽  
T R Geballe ◽  
...  
Keyword(s):  
Amorphous Carbon ◽  
Near Infrared ◽  
Dust Emission ◽  
Infrared Excess ◽  
Object A ◽  
Bolometric Luminosity ◽  
Dust Mass ◽  
Mass Ejection ◽  
Lower Limits ◽  
Hydrogenated Amorphous

ABSTRACT We present an analysis of the evolution of circumstellar dust and molecules in the environment of the very late thermal pulse object V4334 Sgr (Sakurai’s object) over an ∼20-yr period, drawing on ground-, airborne-, and space-based infrared photometry and spectroscopy. The dust emission, which started in 1997, resembles a blackbody that cooled from ∼1200 K in 1998 August to ∼180 K in 2016 July. The dust mass, assuming amorphous carbon, was ∼5 × 10−10 M⊙ in 1998 August, and we estimate that the total dust mass was ∼2 × 10−5 M⊙ by ∼2016. The appearance of a near-infrared excess in 2008 suggests that a new episode of (or renewed) mass-loss began then. We infer lower limits on the bolometric luminosity of the embedded star from that of the dust shell, which rose to ∼16 000 L⊙ before declining to ∼3000 L⊙. There is evidence for weak 6–7 μm absorption, which we attribute to hydrogenated amorphous carbon formed in material ejected by Sakurai’s object during a mass ejection phase that preceded the 1997 event. We detect small hydrocarbon and other molecules in the spectra, and trace the column densities in hydrogen cyanide (HCN) and acetylene (C2H2). We use the former to determine the 12C/13C ratio to be 6.4 ± 0.7, 14 times smaller than the Solar system value.

scholarly journals Spectro-interferometric observations of a sample of Be stars

2019 ◽  
Vol 621 ◽  
pp. A123 ◽  
Author(s):  
Y. R. Cochetti ◽  
C. Arcos ◽  
S. Kanaan ◽  
A. Meilland ◽  
L. S. Cidale ◽  
...  
Keyword(s):  
Critical Velocity ◽  
Velocity Ratio ◽  
Density Wave ◽  
Wave Structure ◽  
Maximum Size ◽  
Rotation Velocity ◽  
Variable Stars ◽  
High Mass ◽  
Be Stars ◽  
Infrared Excess

Context. Be stars are rapid rotators surrounded by a gaseous disk envelope whose origin is still under debate. This envelope is responsible for observed emission lines and large infrared excess. Aims. To progress in the understanding of the physical processes involved in the disk formation, we estimate the disk parameters for a sample of Be stars and search for correlations between these parameters and stellar properties. Methods. We performed spectro-interferometric observations of 26 Be stars in the region of the Brγ line to study the kinematical properties of their disks through the Doppler effect. Observations were performed at the Paranal observatory with the VLTI/AMBER interferometer. This instrument provides high spectral (R ≃ 12 000) and high spatial (θmin = 4 mas) resolutions. Results. We modeled 18 Be stars with emission in the Brγ line. The disk kinematic is described by a quasi-Keplerian rotation law, with the exception of HD 28497 that presents a one-arm density-wave structure. Using a combined sample, we derived a mean value for the velocity ratio V̅/V̅c = 0.75 (where Vc is the critical velocity), and found that rotation axes are probably randomly distributed in the sky. Disk sizes in the line component model are in the range of 2–13 stellar radii and do not correlate with the effective temperature or spectral type. However, we found that the maximum size of a stable disk correlates with the rotation velocity at the inner part of the disk and the stellar mass. Conclusions. We found that, on average, the Be stars of our combined sample do not rotate at their critical velocity. However, the centrifugal force and mass of the star defines an upper limit size for a stable disk configuration. For a given rotation, high-mass Be stars tend to have more compact disks than their low-mass counterparts. It would be interesting to follow up the evolution of the disk size in variable stars to better understand the formation and dissipation processes of their circumstellar disks.

scholarly journals Kilonova/Macronova Emission from Compact Binary Mergers

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Masaomi Tanaka
Keyword(s):  
Gravitational Wave ◽  
Near Infrared ◽  
Expansion Velocity ◽  
Infrared Excess ◽  
Wave Source ◽  
Compact Binary ◽  
Binary Mergers ◽  
Infrared Wavelengths ◽  
Absolute Magnitudes ◽  
Review Current

We review current understanding of kilonova/macronova emission from compact binary mergers (mergers of two neutron stars or a neutron star and a black hole). Kilonova/macronova is emission powered by radioactive decays ofr-process nuclei and it is one of the most promising electromagnetic counterparts of gravitational wave sources. Emission from the dynamical ejecta of ~0.01M⊙is likely to have a luminosity of ~1040–1041 erg s−1with a characteristic timescale of about 1 week. The spectral peak is located in red optical or near-infrared wavelengths. A subsequent accretion disk wind may provide an additional luminosity or an earlier/bluer emission if it is not absorbed by the precedent dynamical ejecta. The detection of near-infrared excess in short GRB 130603B and possible optical excess in GRB 060614 supports the concept of the kilonova/macronova scenario. At 200 Mpc distance, a typical peak brightness of kilonova/macronova with0.01M⊙ejecta is about 22 mag and the emission rapidly fades to >24 mag within ~10 days. Kilonova/macronova candidates can be distinguished from supernovae by (1) the faster time evolution, (2) fainter absolute magnitudes, and (3) redder colors. Since the high expansion velocity (v~0.1–0.2c) is a robust outcome of compact binary mergers, the detection of smooth spectra will be the smoking gun to conclusively identify the gravitational wave source.

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