Evidence of an evolved nature of MWC 349A

Kraus, M.; Arias, María Laura; Cidale, L. S.; Torres, A. F.

doi:10.1093/mnras/staa519

Cited by 14 publications

(14 citation statements)

References 56 publications

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“…13). Emission in the Pfund series is observed in massive YSOs (Bik et al 2005(Bik et al , 2006, sgB[e] stars (Oksala et al 2013;Kraus et al 2020) and LBVs (Oksala et al 2013;Najarro et al 2015). The line widths of both stars are consistent with any of these possibilities; however the ratio of (Brγ/Pf-20) ∼ 2.5 for P57 and P58 is significantly lower than that found for the Pistol star, where the emission arises in a spherical stellar wind ((Brγ/Pf-20) ∼ 10; Najarro et al 2015).…”

Section: Miscellaneous and Uncertain Classificationmentioning

confidence: 74%

Constraining the population of isolated massive stars within the Central Molecular Zone

Clark

Patrick

Najarro

et al. 2021

A&A

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Context. Many galaxies host pronounced circumnuclear starbursts, fuelled by infalling gas. Such activity is expected to drive the secular evolution of the nucleus and generate super winds which enrich the interstellar and intergalactic medium. Moreover, given the intense radiation fields and extreme gas and cosmic ray densities present within such regions, one might question whether star formation proceeds in a different manner to that occurring in more quiescent regions of the galactic disc, potentially leading to a dependence of the stellar initial mass function on the local environment. Aims. To address the physics of circumnuclear starbursts, we are driven to observe the centre of our own Galaxy, which is the only example where individual stars may be resolved. Previous studies have revealed a rich population of very massive stars, found in three young massive clusters as well as being distributed, in apparent isolation, throughout the inner ∼500 pc of the Galaxy. In this paper we investigate the size and composition of the latter cohort in order to constrain its origin and role in the lifecycle of the Galactic Centre. Methods. To accomplish this, we utilised the Very Large Telescope + K-band Multi-Object Spectrograph to obtain homogeneous, high signal-to-noise ratio observations of known and candidate massive stars suitable for spectral classification and quantitative analysis. Results. We identified 17 new isolated massive stars and reclassified a further 19 known examples, leading to a total of at least 83 within the Galactic Centre. Due to the selection criteria employed, these were strongly biased towards stars with powerful stellar winds and/or extensive circumstellar envelopes; as such, we suspect the resultant census to be incomplete. No further stellar clusters, or their tidally stripped remnants, were identified, although an apparent overdensity of very young and massive stars is found to be coincident with the Sgr B1 star forming region. Conclusions. Despite the limitations of the current dataset, the size of the cohort of outlying massive stars within the Galactic Centre is directly comparable to that of the known clusters and, assuming a comparable mass function, is expected to exceed this number. Combining both cluster and isolated populations yields ≳320 spectroscopically classified stars within the Galactic Centre that are sufficiently massive that they might be anticipated to undergo core collapse within the next ∼20 Myr. Given this is almost certainly a substantial underestimate of the true number, the population of massive stars associated with the Galactic Centre appears unprecedented within the Milky Way, and it appears unavoidable that they play a substantial role in the energetics and evolution of this region.

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Section: Miscellaneous and Uncertain Classificationmentioning

confidence: 74%

Constraining the population of isolated massive stars within the Central Molecular Zone

Clark

Patrick

Najarro

et al. 2021

A&A

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“…For the other two, which so far have also been considered as HAeBe candidates (see Table 9), the detection of chemically processed material can hence be regarded as the ultimate proof of their evolved, supergiant nature. These are the objects MWC 137 ([59]) and MWC 349 ( [62]). These results are very promising and encouraging, and they demonstrate that the 13 CO molecular emission provides a solid tool to unambiguously classify a star as either a pre-main sequence or an evolved object.…”

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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“…13). Emission in the Pfund series is observed in massive YSOs (Bik et al 2005(Bik et al , 2006, sgB[e] stars (Oksala et al 2013, Kraus et al 2020 and LBVs (Oksala et al 2013, Najarro et al 2015. The line widths of both stars are consistent with any of these possibilities; however the ratio of (Brγ/Pf-20)∼ 2.5 for P57 and P58 is significantly lower than that found for for the Pistol star, where the emission arises in a spherical stellar wind ((Brγ/Pf-20)∼ 10; Najarro et al 2015).…”

Section: Miscellaneous and Uncertain Classificationmentioning

confidence: 73%

Constraining the population of isolated massive stars within the Central Molecular Zone

Clark,

Patrick,

Najarro

et al. 2021

Preprint

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Context. Many galaxies host pronounced circumnuclear starbursts, fuelled by infalling gas. Such activity is expected to drive the secular evolution of the nucleus and generate super winds, while the intense radiation fields and extreme gas and cosmic ray densities present may act to modify the outcome of star formation with respect to more quiescent galactic regions. Aims. The centre of the Milky Way is the only example of this phenomenon where, by virtue of its proximity, individual stars may be resolved. Previous studies reveal that it hosts a rich population of very massive stars; these are located within three clusters, with an additional cohort dispersed throughout the Central Molecular Zone. In this paper we investigate the size and composition of the latter contingent. Methods. We utilised the VLT+KMOS to obtain homogeneous, high signal-to-noise ratio observations of known and candidate massive stars suitable for spectral classification and quantitative analysis. Results. Including previously identified examples, we find a total of 83 isolated massive stars within the Galactic Centre, which are strongly biased towards objects supporting powerful stellar winds and/or extensive circumstellar envelopes. No further stellar clusters, or their tidally stripped remnants, were identified, although an apparent stellar overdensity is found to be coincident with the Sgr B1 star forming region. Conclusions. The cohort of isolated massive stars within the Central Molecular Zone is directly comparable in size to that of the known clusters and, due to observational biases, is likely highly incomplete at this time. Combining both populations yields 320 spectroscopically classified stars that would be expected to undergo core collapse within the next ∼ 20Myr. Given that this is almost certainly a substantial underestimate of the true number, the population of massive stars associated with the Galactic Centre appears unprecedented amongst star formation complexes within the Milky Way, and it appears probable that they play a substantial role in the energetics and evolution of the nuclear region.

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Evidence of an evolved nature of MWC 349A

Cited by 14 publications

References 56 publications

Constraining the population of isolated massive stars within the Central Molecular Zone

Constraining the population of isolated massive stars within the Central Molecular Zone

A Census of B[e] Supergiants

Constraining the population of isolated massive stars within the Central Molecular Zone

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