Detection of X-ray emission from the young low-mass star Rossiter 137B

Thorne-Żytkow objects (TŻOs) are red supergiants with neutron cores. The energy source in TŻOs with low-mass envelopes (≲8 M⊙) is accretion onto the neutron core, while for TŻOs with massive envelopes (≲14 M⊙) it is nuclear burning via the exotic rp process. TŻOs are expected to form as a result of unstable mass transfer in high-mass X-ray binaries, the direct collision of a neutron star with a massive companion after a supernova or the collision of a neutron star with a low-mass star in a globular cluster. We estimate a birth rate of massive TŻOs in the Galaxy of ∼2 10−4 yr−1. Thus, for a characteristic TŻO lifetime of 105–106 yr there should be 20–200 TŻOs in the Galaxy at present. These can be distinguished from ordinary red supergiants because of anomalously high surface abundances of lithium and rp-process elements, produced in the TŻO interior. The TŻO phase ends when either the star has exhausted its rp-process seed elements or the envelope mass decreases below a critical mass (∼14 M⊙). Then nuclear burning becomes inefficient and a neutrino runaway ensues, leading to the dynamical accretion of matter near the core onto the neutron star and its spin up to spin frequencies of up to ∼100 Hz. The fate of the massive envelope is not entirely clear. If a significant fraction can be accreted onto the core, the formation of a black hole becomes likely. Part of the envelope may collapse into a massive disk which may ultimately become gravitationally unstable and lead to the formation of planets or even low-mass stars. We discuss the various possible outcomes and suggest a possible link between massive TŻOs and soft X-ray transients.

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Proxima Centauri – the nearest planet host observed simultaneously with AstroSat, Chandra, and HST

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2574 ◽

2020 ◽

Vol 498 (3) ◽

pp. 3658-3663

Author(s):

S Lalitha ◽

J H M M Schmitt ◽

K P Singh ◽

P C Schneider ◽

R O Parke Loyd ◽

...

Keyword(s):

Spectral Type ◽

High Energy ◽

Mass Star ◽

Habitable Zone ◽

High Energy Radiation ◽

Energy Radiation ◽

X Ray ◽

Coronal Activity ◽

Low Mass

ABSTRACT Our nearest stellar neighbour, Proxima Centauri, is a low-mass star with spectral type dM5.5 and hosting an Earth-like planet orbiting within its habitable zone. However, the habitability of the planet depends on the high-energy radiation of the chromospheric and coronal activity of the host star. We report the AstroSat, Chandra, and HST observation of Proxima Centauri carried out as part of the multiwavelength simultaneous observational campaign. Using the soft X-ray data, we probe the different activity states of the star. We investigate the coronal temperatures, emission measures and abundance. Finally, we compare our results with earlier observations of Proxima Centauri.

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The corona of GJ 1151 in the context of star–planet interaction

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1982 ◽

2020 ◽

Vol 497 (1) ◽

pp. 1015-1019

Author(s):

G Foster ◽

K Poppenhaeger ◽

J D Alvarado-Gómez ◽

J H M M Schmitt

Keyword(s):

Radio Emission ◽

Low Frequency ◽

Mass Star ◽

Coronal Temperature ◽

X Ray ◽

Upper Limit ◽

Radio Signals ◽

Low Mass ◽

Time Periods

ABSTRACT The low-mass star GJ 1151 has been reported to display variable low-frequency radio emission, which has been interpreted as a signpost of coronal star–planet interactions with an unseen exoplanet. Here we report the first X-ray detection of GJ 1151’s corona based on the XMM–Newton data. We find that the star displays a small flare during the X-ray observation. Averaged over the observation, we detect the star with a low coronal temperature of 1.6 MK and an X-ray luminosity of LX = 5.5 × 1026 erg s−1. During the quiescent time periods excluding the flare, the star remains undetected with an upper limit of $L_{\mathrm{ X},\, \mathrm{ qui}} \le 3.7\times 10^{26}$ erg s−1. This is compatible with the coronal assumptions used in a recently published model for a star–planet interaction origin of the observed radio signals from this star.

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Iron K-Line Emission from X-Ray Binaries

International Astronomical Union Colloquium ◽

10.1017/s0252921100107389 ◽

1988 ◽

Vol 102 ◽

pp. 47-50

Author(s):

K. Masai ◽

S. Hayakawa ◽

F. Nagase

Keyword(s):

Accretion Disk ◽

Radiative Recombination ◽

Characteristic Temperature ◽

Line Emission ◽

Ionization Front ◽

Continuum Radiation ◽

X Ray ◽

Low Mass ◽

X Ray Binaries

AbstractEmission mechanisms of the iron Kα-lines in X-ray binaries are discussed in relation with the characteristic temperature Txof continuum radiation thereof. The 6.7 keV line is ascribed to radiative recombination followed by cascades in a corona of ∼ 100 eV formed above the accretion disk. This mechanism is attained for Tx≲ 10 keV as observed for low mass X-ray binaries. The 6.4 keV line observed for binary X-ray pulsars with Tx> 10 keV is likely due to fluorescence outside the He II ionization front.

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Low‐Mass Star Formation and the Initial Mass Function in IC 348

The Astrophysical Journal ◽

10.1086/306393 ◽

1998 ◽

Vol 508 (1) ◽

pp. 347-369 ◽

Cited By ~ 121

Author(s):

K. L. Luhman ◽

G. H. Rieke ◽

C. J. Lada ◽

E. A. Lada

Keyword(s):

Star Formation ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Mass Star ◽

Low Mass

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Phase lags of quasi-periodic oscillations across source states in the low-mass X-ray binary 4U 1636–53

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stw1271 ◽

2016 ◽

Vol 461 (1) ◽

pp. 79-92 ◽

Cited By ~ 10

Author(s):

Marcio G. B. de Avellar ◽

Mariano Méndez ◽

Diego Altamirano ◽

Andrea Sanna ◽

Guobao Zhang

Keyword(s):

Periodic Oscillations ◽

X Ray ◽

Phase Lags ◽

Low Mass

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X-ray and UV emission of the ultrashort-period, low-mass eclipsing binary system BX Trianguli

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834116 ◽

2018 ◽

Vol 619 ◽

pp. A138

Author(s):

V. Perdelwitz ◽

S. Czesla ◽

J. Robrade ◽

T. Pribulla ◽

J. H. M. M. Schmitt

Keyword(s):

Binary System ◽

Light Curve ◽

Binary Systems ◽

Uv Light ◽

Close Binary ◽

Eclipsing Binary ◽

X Ray ◽

Uv Emission ◽

Low Mass ◽

Orbital Modulation

Context.Close binary systems provide an excellent tool for determining stellar parameters such as radii and masses with a high degree of precision. Due to the high rotational velocities, most of these systems exhibit strong signs of magnetic activity, postulated to be the underlying reason for radius inflation in many of the components. Aims.We extend the sample of low-mass binary systems with well-known X-ray properties. Methods.We analyze data from a singular XMM-Newton pointing of the close, low-mass eclipsing binary system BX Tri. The UV light curve was modeled with the eclipsing binary modeling tool PHOEBE and data acquired with the EPIC cameras was analyzed to search for hints of orbital modulation. Results.We find clear evidence of orbital modulation in the UV light curve and show that PHOEBE is fully capable of modeling data within this wavelength range. Comparison to a theoretical flux prediction based on PHOENIX models shows that the majority of UV emission is of photospheric origin. While the X-ray light curve does exhibit strong variations, the signal-to-noise ratio of the observation is insufficient for a clear detection of signs of orbital modulation. There is evidence of a Neupert-like correlation between UV and X-ray data.

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Early Science from POSSUM: Shocks, turbulence, and a massive new reservoir of ionised gas in the Fornax cluster

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2021.4 ◽

2021 ◽

Vol 38 ◽

Author(s):

C. S. Anderson ◽

G. H. Heald ◽

J. A. Eilek ◽

E. Lenc ◽

B. M. Gaensler ◽

...

Keyword(s):

X Ray ◽

Main Cluster ◽

Rotation Measure ◽

Sky Survey ◽

Low Mass ◽

Fornax Cluster ◽

Depth Enhancement ◽

Projected Distance ◽

Density Regime ◽

New Reservoir

Abstract We present the first Faraday rotation measure (RM) grid study of an individual low-mass cluster—the Fornax cluster—which is presently undergoing a series of mergers. Exploiting commissioning data for the POlarisation Sky Survey of the Universe’s Magnetism (POSSUM) covering a ${\sim}34$ square degree sky area using the Australian Square Kilometre Array Pathfinder (ASKAP), we achieve an RM grid density of ${\sim}25$ RMs per square degree from a 280-MHz band centred at 887 MHz, which is similar to expectations for forthcoming GHz-frequency ${\sim}3\pi$ -steradian sky surveys. These data allow us to probe the extended magnetoionic structure of the cluster and its surroundings in unprecedented detail. We find that the scatter in the Faraday RM of confirmed background sources is increased by $16.8\pm2.4$ rad m−2 within 1 $^\circ$ (360 kpc) projected distance to the cluster centre, which is 2–4 times larger than the spatial extent of the presently detectable X-ray-emitting intracluster medium (ICM). The mass of the Faraday-active plasma is larger than that of the X-ray-emitting ICM and exists in a density regime that broadly matches expectations for moderately dense components of the Warm-Hot Intergalactic Medium. We argue that forthcoming RM grids from both targeted and survey observations may be a singular probe of cosmic plasma in this regime. The morphology of the global Faraday depth enhancement is not uniform and isotropic but rather exhibits the classic morphology of an astrophysical bow shock on the southwest side of the main Fornax cluster, and an extended, swept-back wake on the northeastern side. Our favoured explanation for these phenomena is an ongoing merger between the main cluster and a subcluster to the southwest. The shock’s Mach angle and stand-off distance lead to a self-consistent transonic merger speed with Mach 1.06. The region hosting the Faraday depth enhancement also appears to show a decrement in both total and polarised radio emission compared to the broader field. We evaluate cosmic variance and free-free absorption by a pervasive cold dense gas surrounding NGC 1399 as possible causes but find both explanations unsatisfactory, warranting further observations. Generally, our study illustrates the scientific returns that can be expected from all-sky grids of discrete sources generated by forthcoming all-sky radio surveys.

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