Luminous and Variable Stars in M31 and M33. V. The Upper HR Diagram

Humphreys, R. M.; Davidson, Kris; Hahn, David L.; Martin, John; Weis, Karsten

doi:10.3847/1538-4357/aa7cef

Cited by 25 publications

(30 citation statements)

References 40 publications

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“…A status of a late A-type warm hypergiant has been assigned to this object based on the lack of detected He I emission ( [142]). In contrast to this, He I emission lines were reported by [139], and an effective temperature of 10 000 K has been estimated from the modeling of the stars' spectral energy distribution ( [141]). The position of the object in the near-IR and WISE diagrams coincides with the B[e]SG domain.…”

Section: (J00462108+4213082)mentioning

confidence: 94%

“…As it otherwise fulfills all criteria of a B[e]SG (even displaying CO band emission, [136]), it is included into the list of confirmed B[e]SGs, but keeping in mind that with its A spectral type it is actually a representative of the (though few) A[e]SGs. Recent modeling of the star's spectral energy distribution resulted in an effective temperature estimate of 11 000 K ( [141]), which would point towards a late-B spectral type. The star is reported to display He I, Fe II, and [Fe II] emission and was suggested as B[e]SG star ( [139]).…”

Section: J00452258+4150348mentioning

confidence: 99%

“…The object is not reported in other published spectroscopic investigations to display all B[e]SG characteristics. Instead, it was listed as Fe II emission line star ( [98]) and more recently as LBV candidate ( [141]). This object was first proposed to be a P Cyg-type LBV candidate ( [95]).…”

Section: J00452258+4150348mentioning

confidence: 99%

“…This object was first proposed to be a P Cyg-type LBV candidate ( [95]). With the detection of [Ca II] emission and circumstellar dust ( [98]), and with the determination of an effective temperature of 6600 K ( [141]), it was classified as a warm hypergiant. On the other hand, a B[e]SG classification with a central star of 15 000-20 000 K has been suggested, based on the presence of He I lines displaying P Cyg profiles and the detection of intense CO band emission ( [137]).…”

Section: J00452258+4150348mentioning

confidence: 99%

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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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Section: (J00462108+4213082)mentioning

confidence: 94%

Section: J00452258+4150348mentioning

confidence: 99%

Section: J00452258+4150348mentioning

confidence: 99%

Section: J00452258+4150348mentioning

confidence: 99%

See 2 more Smart Citations

A Census of B[e] Supergiants

Kraus

2019

Galaxies

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“…The reduction process was carried out using IRAF 2 software package tasks. The basic reduction Bonanos et al (2009Bonanos et al ( , 2010 and Humphreys et al (2017b). We show the location of our target stars with red diamonds.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

On the evolutionary state of massive stars in transition phases in M33

Kourniotis

Kraus

Arias

et al. 2018

Monthly Notices of the Royal Astronomical Society

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The advanced stages of several high-mass stars are characterized by episodic mass loss shed during phases of instability. Key for assigning these stars a proper evolutionary state is to assess the composition and geometry of their ejecta alongside the stellar properties. We selected five hot LBV candidates in M33 to refine their classification, investigate their circumstellar environments and explore their evolutionary properties. Being accessible targets in the near-infrared, we conducted medium-resolution spectroscopy with GNIRS/GEMINI in the K−band to investigate their molecular circumstellar environments. Two stars were found to display CO emission, which was modeled to emerge from a circumstellar or circumbinary Keplerian disk/ring. The identification of the carbon isotope 13 C and, for one of the two stars, a significantly low 12 CO/ 13 CO ratio, implies an evolved stellar state. As both CO emission stars are highly luminous and hence do not undergo a red supergiant phase, we suggest that stripping processes and equatorial high-density ejecta due to fast rotation are responsible for the enrichment of the stellar surface with processed material from the core. A candidate B[e]SG displays an absorption CO profile, which may be attributed to a jet or stellar pulsations. The featureless infrared spectra of two stars suggest a low-density gas shell or dissipation of the molecule due to the ionizing temperature of the star. We propose spectroscopic monitoring of our targets to evaluate the stability of the CO molecule and assess the time-dependent dynamics of the circumstellar gas structures.

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How common is LBV S Doradus variability at low metallicity?

Kalari

Dufton

Fraser

2018

A&A

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It remains unclear whether massive star evolution is facilitated by mass loss through stellar winds only, or whether episodic mass loss during an eruptive luminous blue variable (LBV) phase is also significant. LBVs exhibit unique photometric and spectroscopic variability (termed S Dor variables). This may have tremendous implications for our understanding of the first stars, gravitational wave events, and supernovae. A key question here is whether all evolved massive stars passing through the blue supergiant phase are dormant S Dor variables transforming during a brief period, or whether LBVs are truly unique objects. By investigating the OGLE light-curves of 64 B supergiants (Bsgs) in the Small Magellanic Cloud (SMC) on a timescale of three years with a cadence of one night, the incidence of S Dor variables amongst the Bsgs population is investigated. From our sample, we find just one Bsg, AzV 261, that displays the photometric behaviour characteristic of S Doradus variables. We obtain and study a new VLT X-shooter spectrum of AzV 261 in order to investigate whether the object has changed its effective temperature over the last decade. We do not find any effective temperature variations indicating that the object is unlikely to be a LBV S Dor variable. As there is only one previous bona-fide S Dor variable known to be present in the SMC (R 40), we find the maximum duration of the LBV phase in the SMC to be at most ∼few 10 3 yrs, or more likely that canonical Bsgs and S Dor LBVs are intrinsically different objects. We discuss the implications for massive star evolution in low metallicity environments, characteristic of the early Universe.

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Luminous and Variable Stars in M31 and M33. V. The Upper HR Diagram

Cited by 25 publications

References 40 publications

A Census of B[e] Supergiants

A Census of B[e] Supergiants

On the evolutionary state of massive stars in transition phases in M33

How common is LBV S Doradus variability at low metallicity?

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