HIGH-RESOLUTION VLBA OBSERVATIONS OF THREE 7 mm SiO MASERS TOWARD VX Sgr AT FIVE EPOCHS

Jian-jun, SU; Shen, Zhi-Qiang; Chen, X.; Yi, Jiyune; Jiang, Dongrong; Yun, Youngjoo

doi:10.1088/0004-637x/754/1/47

Cited by 14 publications

(13 citation statements)

References 18 publications

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“…Here, we find roughly two order of differences in intensity between the two cases. Similarly, the SiO maser emission (v = 1, J = 1-0) of the three well-known nearby RSGs exhibit systematically larger fluxes than RSGs in Wd1: VY CMa, VX Sgr and NML Cyg exhibit the peak intensities of 5.4 Jy, 31.4 Jy and 2.6 Jy (scaled at 3.5 kpc, Boboltz & Claussen 2004;Zhang et al 2012a;Su et al 2012), while W 237 and W 26 exhibit 1.54 Jy and 0.12 Jy, respectively. However, these differences in intensity between nearby RSGs and RSGs associated with Wd1 are partly due to the uncertainty of distances.…”

Section: Results Of the Sio And H 2 O Maser Observationsmentioning

confidence: 91%

Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated With Massive Clusters

Nakashima

Yung

et al. 2012

ApJ

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We report the results of Australia Telescope Compact Array (ATCA) observations of the Westerlund 1 (Wd1) region in the SiO v = 1, J = 1-0 and H 2 O 6 16 -5 23 maser lines, and we also report the analysis of maser properties of red supergiants (RSGs) associated with 6 massive clusters including Wd1. The primary purpose of this research is to explore possibilities of using maser emission for investigating the nature of massive clusters and associated RSGs. The SiO v = 1, J = 1-0 and H 2 O 6 16 -5 23 maser lines are detected toward 2 of 4 known RSGs in Wd1. The large velocity ranges of maser emission are consistent with the RSG status. RSGs with maser emission tend to exhibit redder log(F 21 /F 12 ) and [K-12.13] colors compared to RSGs with no maser emission. The mass-loss rates derived from dust radiative transfer modeling suggest that RSGs with maser emission tend to exhibit larger mass-loss rates compared to RSGs with no maser emission. In an extended sample of 57 RSGs in 6 massive clusters, detections in the SiO line tend to homogeneously distribute in absolute luminosity L, whereas those in the H 2 O line tend to distribute in a region with large L values.

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Section: Results Of the Sio And H 2 O Maser Observationsmentioning

confidence: 91%

Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated With Massive Clusters

Nakashima

Yung

et al. 2012

ApJ

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“…For example, Richards et al (2012) estimated the radius of the H 2 O maser cloud in VX Sgr to be an order of magnitude larger than those around known AGB stars. Arroyo-Torres et al (2013), based on data from Chiavassa et al (2010) and Su et al (2012), also found that the SiO masers of VX Sgr are located at ~3 stellar radii, while the SiO masers in AGB stars are mostly located at ~2 stellar radii. On the other hand, these results for VX Sgr are consistent with those obtained for other RHGs, for example S Per (Richards et al 2012) andAH Sco (Arroyo-Torres et al 2013).…”

Section: Introductionmentioning

confidence: 93%

The nature of VX Sagitarii

Tabernero

Dorda

Negueruela

et al. 2021

A&A

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Aims. We present a spectroscopic analysis of the extremely luminous red star VX Sgr based on high-resolution observations combined with AAVSO light curve data. Given the puzzling characteristics of VX Sgr, we explore three scenarios for its nature: a massive red supergiant (RSG) or red hypergiant (RHG), a Thorne Żytkow object, and an extreme asymptotic giant branch (AGB) star. Methods. Sampling more than one whole cycle of photometric variability, we derive stellar atmospheric parameters by using state-of-the-art PHOENIX atmospheric models. We compare them to optical and near-infrared spectral types. We report on some key features due to neutral elemental atomic species such as Li I, Ca I, and Rb I. Results. We provide new insights into its luminosity, its evolutionary stage, and its pulsation period. Based on all the data, there are two strong reasons to believe that VX Sgr is some sort of extreme AGB star. Firstly, it has Mira-like behaviour during active phases. VX Sgr shows light variation with amplitude that is much larger than any known RSG and clearly larger than all RHGs. In addition, it displays Balmer line emission and, as shown here for the first time, line doubling of its metallic spectrum at maximum light, both characteristics typical of Miras. Secondly, unlike any known RSG or RHG, VX Sgr displays strong Rb I lines. In addition to the photospheric lines that are sometimes seen, it always shows circumstellar components whose expansion velocity is compatible with that of the OH masers in the envelope, demonstrating a continuous enrichment of the outer atmosphere with s-process elements, a behaviour that can only be explained by a third dredge-up during the thermal pulse phase.

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“…Similarly, Su et al (2012) found that SiO maser emission forms a ring with a very narrow range of line-of-sight velocities, while Danchi et al (1994) and Monnier et al (2004) used infrared interferometry to infer the presence of a centrosymmetric structure in dust emission with an inner radius of around 60 mas. Schuster et al (2006) found a similar emission region to our data but did not see any significant asymmetry in the optical, attributing a slight deviation from circular symmetry to CCD bleeding.…”

Section: Discussionmentioning

confidence: 98%

precision: a fast python pipeline for high-contrast imaging – application to SPHERE observations of the red supergiant VX Sagitariae

Scicluna

Kemper

Siebenmorgen

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The search for extrasolar planets has driven rapid advances in instrumentation, resulting in cameras such as SPHERE at the VLT, GPI at Gemini South and SCExAO at Subaru, capable of achieving very high contrast (∼ 10 6 ) around bright stars with small inner working angles (∼ 0. 1). The optimal exploitation of data from these instruments depends on the availability of easy-to-use software to process and analyse their data products. We present a pure-python pipeline, precision, which provides fast, memory-efficient reduction of data from the SPHERE/IRDIS near-infrared imager, and can be readily extended to other instruments. We apply precision to observations of the extreme red supergiant VX Sgr, the inner outflow of which is revealed to host complex, asymmetric structure in the near-IR. In addition, optical polarimetric imaging reveals clear extended polarised emission on ∼ 0.5 scales which varies significantly with azimuth, confirming the asymmetry. While not conclusive, this could suggest that the ejecta are confined to a disc or torus, which we are viewing nearly face on, although other non-spherical or clumpy configurations remain possible. VX Sgr has no known companions, making such a geometry difficult to explain, as there is no obvious source of angular momentum in the system.

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HIGH-RESOLUTION VLBA OBSERVATIONS OF THREE 7 mm SiO MASERS TOWARD VX Sgr AT FIVE EPOCHS

Cited by 14 publications

References 18 publications

Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated With Massive Clusters

Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated With Massive Clusters

The nature of VX Sagitarii

precision: a fast python pipeline for high-contrast imaging – application to SPHERE observations of the red supergiant VX Sagitariae

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