- ID:
- ivo://CDS.VizieR/J/A+A/555/A64
- Title:
- Identifying gaps in flaring Herbig Ae/Be disks
- Short Name:
- J/A+A/555/A64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolution of protoplanetary disks towards mature planetary systems is expected to include the formation of 'gaps' in the disk possibly due to planet formation. We studied the disks of four key intermediate mass (Herbig Ae/Be) stars in order to understand the influence of gaps to their observational appearance. We investigate mid-infrared images and perform radiative transfer modeling to examine the radial distribution of dust and PAHs. Our solutions constrain the sizes of the gaps. For one particular object, HD 97048, this is the first detection of a disk gap. The large gaps deplete the entire population of silicate particles with temperatures suitable for prominent mid-infrared feature emission, while small carbonaceous grains and PAHs can still show prominent emission at mid-infrared wavelengths. The absence of silicate emission features is due to the presence of large gaps in the critical temperature regime. Our results suggest that many, if not all Herbig disks with weak or no silicate features in the spectrum are disks with large gaps and can be characterized as (pre-)transitional. We conclude that the evolution of Herbig stars follows two different paths. Competition between the timescales of inner versus outer disk evolution determine whether young protoplanetary disks evolve into transitional disks (due to planet formation in the inner disk) or into flat disks (due to the grain growth and dust settling in the outer disk).
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/463/1162
- Title:
- Infrared photometry of Be stars
- Short Name:
- J/MNRAS/463/1162
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we have collected data for almost all Be stars known so far (1991 sources in total) and photometrically study their infrared properties. 2MASS, WISE, IRAS and Akari data are analysed. It is shown from several two-colour diagrams that from 1 to 60um, infrared excesses for the majority of Be stars are mainly due to the free-free emission or the bound-free emission from proton-electron scattering, while for only a small number of Be stars their infrared excess originates from dust thermal radiation or is caused by the nebulosity/binarity effects. However, in the wavelength range 3.4-12um (the WISE W1, W2 and W3 bands), some Be stars show the properties of dust thermal radiation, which is probably due to silicate dust emission and/or polycyclic aromatic hydrocarbon emission. In addition, it is found in this paper that infrared colour excesses indeed increase with wavelength for Be stars. However, no correlations between infrared colours and spectral type can be found for Be stars. Furthermore, several stars have very large infrared excesses in the near-infrared. The reasons for such infrared excesses are given in more detail.
- ID:
- ivo://CDS.VizieR/J/ApJ/654/527
- Title:
- Interferometric observations of northern Be stars
- Short Name:
- J/ApJ/654/527
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first K'-band, long-baseline interferometric observations of the northern Be stars {gamma} Cas, {phi} Per, {zeta} Tau, and {kappa} Dra. The measurements were made with multiple telescope pairs of the CHARA Array interferometer and in every case the observations indicate that the circumstellar disks of the targets are resolved. We fit the interferometric visibilities with predictions from a simple disk model that assumes an isothermal gas in Keplerian rotation. We derive fits of the four model parameters (disk base density, radial density exponent, disk normal inclination, and position angle) for each of the targets.
- ID:
- ivo://CDS.VizieR/J/A+A/545/A130
- Title:
- Interferometry of {alpha} Eri
- Short Name:
- J/A+A/545/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectrally resolved long-baseline optical/IR interferometry of rotating stars opens perspectives to investigate their fundamental parameters and the physical mechanisms that govern their interior, photosphere, and circumstellar envelope structures. Aims. Based on the signatures of stellar rotation on observed interferometric wavelength-differential phases, we aim to measure angular diameters, rotation velocities, and orientation of stellar rotation axes.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A140
- Title:
- IPHAS-selected classical Be stars
- Short Name:
- J/A+A/591/A140
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a semi-automatic procedure to obtain fundamental physical parameters and distances of classical Be (CBe) stars, based on the Barbier-Chalonge-Divan (BCD) spectrophotometric system. Our aim is to apply this procedure to a large sample of CBe stars detected by the IPHAS photometric survey, to determine their fundamental physical parameters and to explore their suitability as galactic structure tracers. In this paper we describe the methodology used and the validation of the procedure by comparing our results with those obtained from different independent astrophysical techniques for subsamples of stars in common with other studies. We also present a test case study of the galactic structure in the direction of the Perseus Galactic Arm, in order to compare our results with others recently obtained with different techniques and the same sample of stars. We did not find any significant clustering of stars at the expected positions of the Perseus and Outer Galactic Arms, in agreement with previous studies in the same area that we used for verification.
- ID:
- ivo://CDS.VizieR/J/other/NewA/9.509
- Title:
- IRAS observations of Be stars
- Short Name:
- J/other/NewA/9.5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The IRAS associations for 193 Be stars are identified in this paper. From the infrared colors, the IRAS low-resolution spectra (LRS) and the spectral types, some physical properties and environment of the samples are discussed. It can be concluded that not only free-free emission or free-bound emission from the circumstellar ionized gas can be responsible for the large IR excesses of Be stars as suggested previously, but also, for some Be stars, thermal radiation from the circumstellar dust and/or nebula around the star can produce large IR excess as well. It is also found that the far IR excess of Be stars increases.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A110
- Title:
- IR nebulae around bright massive stars
- Short Name:
- J/A+A/618/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent studies show that more than 70% of massive stars do not evolve as effectively single stars, but as members of interacting binary systems. The evolution of these stars is thus strongly altered compared to similar but isolated objects. We investigate the occurrence of parsec-scale mid-infrared nebulae around early-type stars. If they exist over a wide range of stellar properties, one possible overarching explanation is non-conservative mass transfer in binary interactions, or stellar mergers. For ~3850 stars (all OBA stars in the Bright Star Catalogue (BSC, Cat. V/50), Be stars, BeXRBs, and Be+sdO systems), we visually inspect WISE 22um images. Based on nebular shape and relative position, we distinguish five categories: offset bow shocks structurally aligned with the stellar space velocity, unaligned offset bow shocks, and centered, unresolved, and not classified nebulae. In the BSC, we find that 28%, 13%, and 0.4% of all O, B, and A stars, respectively, possess associated infrared (IR) nebulae. Additionally, 34/234 Be stars, 4/72 BeXRBs, and 3/17 Be+sdO systems are associated with IR nebulae. Aligned or unaligned bow shocks result from high relative velocities between star and interstellar medium (ISM) that are dominated by the star or the ISM, respectively. About 13% of the centered nebulae could be bow shocks seen head- or tail-on. For the rest, the data disfavor explanations as remains of parental disks, supernova remnants of a previous companion, and dust production in stellar winds. The existence of centered nebulae also at high Galactic latitudes strongly limits the global risk of coincidental alignments with condensations in the ISM. Mass loss during binary evolution seems a viable mechanism for the formation of at least some of these nebulae. In total, about 29% of the IR nebulae (2% of all OBA stars in the BSC) may find their explanation in the context of binary evolution.
68. Kappa Dra
- ID:
- ivo://CDS.VizieR/J/A+AS/107/403
- Title:
- Kappa Dra
- Short Name:
- J/A+AS/107/403
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/ApJ/768/128
- Title:
- K-band calibrated visibilities of 24 Be stars
- Short Name:
- J/ApJ/768/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a high angular resolution survey of circumstellar disks around 24 northern sky Be stars. The K-band continuum survey was made using the CHARA Array long baseline interferometer (baselines of 30-331m). The interferometric visibilities were corrected for the flux contribution of stellar companions in those cases where the Be star is a member of a known binary or multiple system. For those targets with good (u, v) coverage, we used a four-parameter Gaussian elliptical disk model to fit the visibilities and to determine the axial ratio, position angle, K-band photospheric flux contribution, and angular diameter of the disk's major axis. For the other targets with relatively limited (u, v) coverage, we constrained the axial ratio, inclination angle, and/or disk position angle where necessary in order to resolve the degeneracy between possible model solutions. We also made fits of the ultraviolet and infrared spectral energy distributions (SEDs) to estimate the stellar angular diameter and infrared flux excess of each target. The mean ratio of the disk diameter (measured in K-band emission) to stellar diameter (from SED modeling) is 4.4 among the 14 cases where we reliably resolved the disk emission, a value which is generally lower than the disk size ratio measured in the higher opacity H{alpha} emission line. We estimated the equatorial rotational velocity from the projected rotational velocity and disk inclination for 12 stars, and most of these stars rotate close to or at the critical rotational velocity.
- ID:
- ivo://CDS.VizieR/J/A+AS/129/289
- Title:
- Long-term spectrophotometry of Be stars
- Short Name:
- J/A+AS/129/289
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The long-term spectrophotometric variations of 49 Be stars are studied using the U and V magnitudes of the UBV system, the total Balmer discontinuity D and the visible gradient {Phi}_rb_. BCD (Barbier-Chalonge-Divan, see Chalonge & Divan, 1952AnAp...15..201C) spectrophotometric and photometric data in five different photometric systems, obtained in most cases since 1950 and reduced to the BCD system, were used. The (U,D), (V,D), ({Phi}_rb_,D) and ({Phi}_rb_,V) correlations obtained differ from star to star and they can be single or double-valued. They differ clearly for Be phases or Be-shell phases. Be stars with small V.sin(i) showing the "spectrophotometric shell behaviour": D>D*, were found. This finding implies either that strongly flattened models of circumstellar envelopes are in doubt for these stars, or that not all Be stars are rapid rotators. Comparison of observed variations with those predicted for model Be stars with spherical circumstellar envelopes of variable densities and dimensions implies that spectrophotometric patterns of Be phases are due to circumstellar envelopes in low opacity regimes, while those of spectrophotometric shell phases are due to circumstellar envelopes in high opacity regimes. In a given star, the envelope regions responsible for the observed variations of D and {Phi}_rb_ in spectrophotometric shell phases seem to be smaller and denser than those producing the observed variations of these parameters in spectrophotometric Be phases. The high positive RV found in strong shell phases might favor the formation of compact circumstellar layers near the star.
