A statistical spectropolarimetric study of Herbig Ae/Be stars

Ababakr, K. M.; Oudmaijer, R. D.

doi:10.1093/mnras/stx1891

Cited by 39 publications

(39 citation statements)

References 45 publications

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“…The data is shown in Table 5. We note that Ababakr et al (2017) also observed a disc in this object through spectropolarimetry, inclined at 146 deg. However, in the interest of consistency with the previous measurement, we use the disc inclination of 80 deg from Navarete et al (2015).…”

Section: Alignment With Discssupporting

confidence: 57%

A pilot survey of the binarity of Massive Young Stellar Objects withK-band adaptive optics

Pomohaci

Oudmaijer

Goodwin

2019

Monthly Notices of the Royal Astronomical Society

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We present the first search for binary companions of Massive Young Stellar Objects (MYSOs) using AO-assisted K band observations, with NaCo at the VLT. We have surveyed 32 MYSOs from the RMS catalogue, probing the widest companions, with a physical separation range of 400 -46,000 au, within the predictions of models and observations for multiplicity of MYSOs. Statistical methods are employed to discern whether these companions are physical rather than visual binaries. We find 18 physical companions around 10 target objects, amounting to a multiplicity fraction of 31±8% and a companion fraction of 53±9%. For similar separation and mass ratio ranges, MYSOs seem to have more companions than T Tauri or O stars, respectively. This suggests that multiplicity increases with mass and decreases with evolutionary stage. We compute very rough estimates for the mass ratios from the K band magnitudes, and these appear to be generally larger than 0.5. This is inconsistent with randomly sampling the IMF, as predicted by the binary capture formation theory. Finally, we find that MYSOs with binaries do not show any different characteristics to the average MYSO in terms of luminosity, distance, outflow or disc presence.

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Section: Alignment With Discssupporting

confidence: 57%

A pilot survey of the binarity of Massive Young Stellar Objects withK-band adaptive optics

Pomohaci

Oudmaijer

Goodwin

2019

Monthly Notices of the Royal Astronomical Society

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“…Based on the break in accretion rates, we can move this boundary to a critical mass of 4M , remarkably close, but not perfectly so, to the boundary of around B7/8 put forward by Ababakr et al (2017). It is thus implied that there is a transition from magnetically controlled accretion in lowmass HAeBes to another accretion mechanism in high-mass HAeBes at around 4 M .…”

Section: On the Use Of Line Emission As Accretion Rate Diagnosticsupporting

confidence: 54%

“…In contrast, the very different effects observed towards the Herbig Be stars were more consistent with disks reaching onto the central star -hinting at a different accretion mechanism in those. The large sample by Ababakr et al (2017) allowed them to identify the transition region to be around spectral type B7/8.…”

Section: Discussionmentioning

confidence: 99%

The accretion rates and mechanisms of Herbig Ae/Be stars

Wichittanakom

Oudmaijer

Fairlamb

et al. 2020

Monthly Notices of the Royal Astronomical Society

126

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This work presents a spectroscopic study of 163 Herbig Ae/Be stars. Amongst these, we present new data for 30 objects. Stellar parameters such as temperature, reddening, mass, luminosity and age are homogeneously determined. Mass accretion rates are determined from Hα emission line measurements. Our data is complemented with the X-Shooter sample from previous studies and we update results using Gaia DR2 parallaxes giving a total of 78 objects with homogeneously determined stellar parameters and mass accretion rates. In addition, mass accretion rates of an additional 85 HAeBes are determined. We confirm previous findings that the mass accretion rate increases as a function of stellar mass, and the existence of a different slope for lower and higher mass stars respectively. The mass where the slope changes is determined to be 3.98 +1.37 −0.94 M . We discuss this break in the context of different modes of disk accretion for low-and high mass stars. Because of their similarities with T Tauri stars, we identify the accretion mechanism for the late-type Herbig stars with the Magnetospheric Accretion. The possibilities for the earlier-type stars are still open, we suggest the Boundary Layer accretion model may be a viable alternative. Finally, we investigated the mass accretion -age relationship. Even using the superior Gaia based data, it proved hard to select a large enough sub-sample to remove the mass dependency in this relationship. Yet, it would appear that the mass accretion does decline with age as expected from basic theoretical considerations.

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“…The latter have emission-line spectra with numerous forbidden emission lines from [Fe II] and [O I] alike the B[e]SGs, and the stars are surrounded by significant amounts of circumstellar dust within their massive accretion disks causing considerable IR excess emission, just as the B[e]SGs. Hence, it is not surprising that confusion exists about the proper classification for a number of objects within this luminosity domain of 4.0 < log L/L < 4.5, and that Galactic B[e]SG candidates also appear as candidates in catalogs of HAeBe stars (see, e.g., [160]). In the absence of clear indications for infall of material, which is a typical characteristic of pre-main sequence stars, alternative discriminators for the classification of such objects are needed.…”

Section: Galactic Objectsmentioning

confidence: 99%

A Census of B[e] Supergiants

Kraus

2019

Galaxies

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Stellar evolution theory is most uncertain for massive stars. For reliable predictions of the evolution of massive stars and their final fate, solid constraints on the physical parameters, and their changes along the evolution and in different environments, are required. Massive stars evolve through a variety of short transition phases, in which they can experience large mass-loss either in the form of dense winds or via sudden eruptions. The B[e] supergiants comprise one such group of massive transition objects. They are characterized by dense, dusty disks of yet unknown origin. In the Milky Way, identification and classification of B[e] supergiants is usually hampered by their uncertain distances hence luminosities, and by the confusion of low-luminosity candidates with massive pre-main sequence objects. The extragalactic objects are often mistaken as quiescent or candidate luminous blue variables, with whom B[e] supergiants share a number of spectroscopic characteristics. In this review, proper criteria are provided, based on which B[e] supergiants can be unambiguously classified and separated from other high luminosity post-main sequence stars and pre-main sequence stars. Using these criteria, the B[e] supergiant samples in diverse galaxies are critically inspected, to achieve a reliable census of the current population.In the HR diagram these objects are all found beyond the main-sequence and with luminosities spreading from about log L/L ∼ 4 to about log L/L ∼ 6 implying that they are all evolved, massive stars. This luminosity range was determined from the sample residing in the Magellanic Clouds (MCs), for which the luminosity determination is unquestionable, due to the low extinction towards the MCs and their well constraint distances. The classification of Galactic objects as supergiants bears much higher uncertainties due to their often poorly constraint distances hence luminosities. We will come back to this issue in Section 4.4.The position of the MC sample in the HR diagram is shown in Figure 1 for the values of luminosity and effective temperature listed in Table 1. The stellar parameters (effective temperature T eff , visual magnitude V, and color excess E(B − V)) of the sample have been taken from the references listed in the last column of Table 1. For the calculations of the luminosities, distance moduli of 18.5 and 18.9 mag for the Large respectively Small Magellanic Clouds have been utilized (see the review paper by Humphreys, this volume) along with bolometric corrections from [29].The presence of dust around an early-type (typically of spectral type B) supergiant, along with the often pure emission-line spectra with numerous forbidden lines predominantly of [Fe II] and [O I] finally resulted in the designation of these objects as B[e] supergiants (B[e]SGs) 1 . 1 Note that these objects have previously been abbreviated sgB[e] ([24]), to separate them from other stars showing the B[e] phenomenon. We prefer the designation B[e]SG, to be in line with the naming and abbreviation of other type o...

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A statistical spectropolarimetric study of Herbig Ae/Be stars

Cited by 39 publications

References 45 publications

A pilot survey of the binarity of Massive Young Stellar Objects withK-band adaptive optics

A pilot survey of the binarity of Massive Young Stellar Objects withK-band adaptive optics

The accretion rates and mechanisms of Herbig Ae/Be stars

A Census of B[e] Supergiants

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