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 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.

Near-Infrared Photometry of Southern Galactic Wolf-Rayet Stars

1982 ◽  
Vol 99 ◽  
pp. 67-72
Author(s):  
C. Sterken ◽  
C. de Loore
Keyword(s):  
Infrared Radiation ◽  
Interstellar Dust ◽  
Near Infrared ◽  
Thermal Emission ◽  
Dust Emission ◽  
Circumstellar Dust ◽  
Infrared Photometry ◽  
Energy Distributions ◽  
Circumstellar Shell

Allen et al. (1972) observed 40 WR stars in the |1.6µ| and |2.2µ| bands, and found evidence of interstellar dust emission in the WC9 stars Ve 2–45, AS320 and HD 313643. Hackwell et al. (1974) reported 2.3 to 23 µ photometry of 19 WR stars and concluded that the excess infrared radiation from the Wolf-Rayet stars (except for the WC9 stars) could be explained by free-free emission from a hot circumstellar shell. Gehrz and Hackwell (1974) found from 2.3 to 23 µ photometry that three out of four WC stars appear to be embedded in thick circumstellar dust (graphite) shells, and concluded that WC9 stars may form a distinct Wolf-Rayet class. Cohen et al. (1975) derived energy distributions of 23 Wolf-Rayet stars from 3µ-11µ scanner spectrophotometry and infrared photometry, and concluded that WN stars show only free-free emission whereas only WC stars show dust. The excesses in WC9 stars are interpreted as thermal emission by graphite grains.

scholarly journals Modeling of Circumstellar Dust by the DUSTY Code

2011 ◽  
Vol 7 (S282) ◽  
pp. 247-250
Author(s):  
Tomislav Jurkić ◽  
Dubravka Kotnik-Karuza
Keyword(s):  
Near Infrared ◽  
Dynamical Behaviour ◽  
Light Curves ◽  
Young Stellar Objects ◽  
Numerical Code ◽  
Circumstellar Dust ◽  
Be Stars ◽  
Stellar Objects ◽  
Near Ir ◽  
Dust Temperature

AbstractWe present a circumstellar dust model around the symbiotic Mira RR Tel obtained by modeling the near-infrared JHKL magnitudes and ISO spectra. In order to follow the evolution of infrared colours in time, the published JHKL magnitudes were corrected by removing the Mira pulsations. The RR Tel light curves show three obscuration events in the near-IR. Using the simultaneously available JHKL magnitudes and ISO spectra in three different epochs, we obtained SEDs in the near- and mid-IR spectral region (1-20 μm) in epochs with and without obscuration.The DUSTY numerical code was used to solve the radiative transfer and to determine the circumstellar dust properties of the inner dust regions around the Mira, assuming a spherical dust temperature distribution in its close neighbourhood. The physical properties of the dust, mass loss and optical depth during intervals with and without obscuration have been obtained. Both JHKL and ISO observations during the obscuration period can be reproduced with a spherical dust envelope, while ISO spectra outside obscuration show a different behaviour. The dynamical behaviour of the circumstellar dust was obtained by modeling the JHKL magnitudes observed during the span of more than 30 years.The DUSTY code was also successfully applied in the modeling of circumstellar dust envelopes of young stellar objects, such as Herbig Ae/Be stars.

The IGRINS YSO Survey II: Veiling Spectra of Pre-main-sequence Stars in Taurus-Auriga

2021 ◽  
Vol 922 (1) ◽  
pp. 27
Author(s):  
Benjamin Kidder ◽  
Gregory Mace ◽  
Ricardo López-Valdivia ◽  
Kimberly Sokal ◽  
Victoria E. Catlett ◽  
...  
Keyword(s):  
Near Infrared ◽  
Thermal Emission ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Class Iii ◽  
Infrared Excess ◽  
Stellar Objects ◽  
Star Forming ◽  
Infrared Spectrometer ◽  
Low Mass

Abstract We present measurements of the H- and K-band veiling for 141 young stellar objects (YSOs) in the Taurus-Auriga star-forming region using high-resolution spectra from the Immersion Grating Near-Infrared Spectrometer. In addition to providing measurements of r H and r K , we produce low-resolution spectra of the excess emission across the H and K bands. We fit temperatures to the excess spectra of 46 members of our sample and measure near-infrared excess temperatures ranging from 1200–2200 K, with an average of 1575 ± 225 K. We compare the luminosity of the excess continuum emission in Class II and Class III YSOs and find that a number of Class III sources display a significant amount of excess flux in the near-infrared. We conclude that the mid-infrared SED slope, and therefore young stellar object classification, is a poor predictor of the amount of near-infrared veiling. If the veiling arises in thermal emission from dust, its presence implies a significant amount of remaining inner-disk (<1 au) material in these Class III sources. We also discuss the possibility that the veiling effects could result from massive photospheric spots, unresolved binary companions, or accretion emission. Six low-mass members of our sample contain a prominent feature in their H-band excess spectra that is consistent with veiling from cool photospheric spots.

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 Massive pre-main sequence stars in M17

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Maria C. Ramirez-Tannus ◽  
Lex Kaper ◽  
Bram B. Ochsendorf ◽  
Lucas E. Ellerbroek
Keyword(s):  
Physical Properties ◽  
Massive Star ◽  
Main Sequence ◽  
Near Infrared ◽  
Band Head ◽  
Emission Lines ◽  
Spectral Features ◽  
Main Sequence Stars ◽  
Infrared Excess ◽  
Star Forming

AbstractWe have obtained optical to near-infrared (300-2500 nm) VLT/X-shooter spectra of six candidate mYSOs, deeply embedded in the massive star forming region M17. These mYSO candidates have been identified based on their infrared excess and spectral features (double-peaked emission lines, CO band-head emission) indicating the presence of a disk (Hanson et al. 1997). In most cases, we detect a photospheric spectrum allowing us to measure the physical properties of the mYSOs and to confirm their PMS nature.

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 Discovery of 2716 hot emission-line stars from LAMOST DR5

2021 ◽  
Vol 21 (11) ◽  
pp. 288
Author(s):  
Baskaran Shridharan ◽  
Blesson Mathew ◽  
Sabu Nidhi ◽  
Ravikumar Anusha ◽  
Roy Arun ◽  
...  
Keyword(s):  
Emission Line ◽  
Near Infrared ◽  
Community Study ◽  
Be Stars ◽  
Mid Infrared ◽  
Data Release ◽  
Homogeneous Set ◽  
Stellar Parameter ◽  
Infrared Wavelengths

Abstract We present a catalog of 3339 hot emission-line stars (ELSs) identified from 451 695 O, B and A type spectra, provided by LAMOST Data Release 5 (DR5). We developed an automated Python routine that identified 5437 spectra having a peak between 6561 and 6568 Å. False detections and bad spectra were removed, leaving 4138 good emission-line spectra of 3339 unique ELSs. We re-estimated the spectral types of 3307 spectra as the LAMOST Stellar Parameter Pipeline (LASP) did not provide accurate spectral types for these emission-line spectra. As Herbig Ae/Be stars exhibit higher excess in near-infrared and mid-infrared wavelengths than classical Ae/Be stars, we relied on 2MASS and WISE photometry to distinguish them. Finally, we report 1089 classical Be, 233 classical Ae and 56 Herbig Ae/Be stars identified from LAMOST DR5. In addition, 928 B[em]/A[em] stars and 240 CAe/CBe potential candidates are identified. From our sample of 3339 hot ELSs, 2716 ELSs identified in this work do not have any record in the SIMBAD database and they can be considered as new detections. Identification of such a large homogeneous set of emission-line spectra will help the community study the emission phenomenon in detail without worrying about the inherent biases when compiling from various sources.

scholarly journals Near Infrared Spectroscopic Observations of Early-type Be Stars

2000 ◽  
Vol 175 ◽  
pp. 468-471 ◽  
Author(s):  
N. M. Ashok ◽  
D. P. K. Banerjee
Keyword(s):  
Emission Line ◽  
Infrared Spectra ◽  
Near Infrared ◽  
Be Stars ◽  
Early Type ◽  
Line Flux ◽  
Near Infrared Spectra ◽  
Medium Resolution ◽  
Significant Strength ◽  
Lower Temperature

AbstractThe medium resolution (R=1000) near infrared spectra of 30 early type Be stars obtained during the period October 1998-April 1999 are presented. The Paschen β and Brackett γ lines are seen in emission in majority of these stars. The higher order Brackett series lines from m=10 to 19 are detected in emission with significant strength compared to the Brackett γ emission line flux indicating the effect of optical depth. The Fe II line at 1.6873μm is detected in a small number of stars indicating existence of higher density and lower temperature emission zone.

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