The UV Emission of Stars in the LAMOST Survey. I. Catalogs

Bai, Yu; Liu, Jifeng; Wicker, James; Wang, Song; Guo, Jincheng; Qin, Yuxiang; He, Lin; Wang, Jianling; Wu, Yue; Dong, Yiqiao; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Cao, Zihuang

doi:10.3847/1538-4365/aaaab9

Cited by 25 publications

(21 citation statements)

References 64 publications

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“…However, the spectral energy distribution (SED) is best fit with an effective temperature of 6000 K. To exclude identification issues, we double checked the identifications of the LAMOST spectrum and the photometry employed for the SED fitting; no misidentifications were detected. In the literature, we also find widely different effective temperature estimates for this star: 5325 K (Ammons et al 2006), 6210 K (Stassun et al 2019), 6785 K (Bai et al 2019), 7950 K (Xiang et al 2019), and 9500 K (Bai et al 2018). The wide range of different temperature values points towards a spectroscopic binary system observed at different phases.…”

Section: Colour-magnitude Diagrammentioning

confidence: 59%

New mercury-manganese stars and candidates from LAMOST DR4

Paunzen

Hümmerich

Bernhard

2021

A&A

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Aims. The present work presents our efforts at identifying new mercury-manganese (HgMn/CP3) stars using spectra obtained with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Methods. Suitable candidates were searched for among pre-selected early-type spectra from LAMOST DR4 using a modified version of the MKCLASS code that probes several Hg ii and Mn ii features. The spectra of the resulting 332 candidates were visually inspected. Using parallax data and photometry from Gaia DR2, we investigated magnitudes, distances from the Sun, and the evolutionary status of our sample stars. We also searched for variable stars using diverse photometric survey sources. Results. We present 99 bona fide CP3 stars, 19 good CP3 star candidates, and seven candidates. Our sample consists of mostly new discoveries and contains, on average, the faintest CP3 stars known (peak distribution 9.5 ≤ G ≤ 13.5 mag). All stars are contained within the narrow spectral temperature-type range from B6 to B9.5, in excellent agreement with the expectations and the derived mass estimates (2.4 ≤ M ⊙ ≤ 4 for most objects). Our sample stars are between 100 Myr and 500 Myr old and cover the whole age range from zero-age to terminal-age main sequence. They are almost homogeneously distributed at fractional ages on the main sequence ≤ 80 %, with an apparent accumulation of objects between fractional ages of 50 % to 80 %. We find a significant impact of binarity on the mass and age estimates. Eight photometric variables were discovered, most of which show monoperiodic variability in agreement with rotational modulation. Conclusions. Together with the recently published catalogue of APOGEE CP3 stars, our work significantly increases the sample size of known Galactic CP3 stars, paving the way for future in-depth statistical studies.

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Section: Colour-magnitude Diagrammentioning

confidence: 59%

New mercury-manganese stars and candidates from LAMOST DR4

Paunzen

Hümmerich

Bernhard

2021

A&A

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“…They do not detect an X-ray flux with Swift, but do detect a small N U V excess with GALEX for this system. They use work by Bai et al (2018) to tentatively suggest that this system has an N U V excess consistent with the distribution of values in red giants, and therefore is unlikely to have significant ongoing accretion.…”

Section: Discussionmentioning

confidence: 89%

Rotationally Driven Ultraviolet Emission of Red Giant Stars

Dixon,

Tayar,

Stassun

2020

Preprint

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Main sequence stars exhibit a clear rotation-activity relationship, in which rapidly rotating stars drive strong chromospheric/coronal ultraviolet and X-ray emission. While the vast majority of red giant stars are inactive, a few percent exhibit strong ultraviolet emission. Here we use a sample of 133 red giant stars observed by SDSS APOGEE and GALEX to demonstrate an empirical relationship between N U V excess and rotational velocity (v sin i). Beyond this simple relationship, we find that N U V excess also correlates with rotation period and with Rossby number in a manner that shares broadly similar trends to those found in M dwarfs, including activity saturation among rapid rotators. Our data also suggest that the most extremely rapidly rotating giants may exhibit so-called "super-saturation", which could be caused by centrifugal stripping of these stars rotating at a high fraction of breakup speed. As an example application of our empirical rotation-activity relation, we demonstrate that the N U V emission observed from a recently reported system comprising a red giant with a black hole companion is fully consistent with arising from the rapidly rotating red giant in that system. Most fundamentally, our findings suggest a common origin of chromospheric activity in rotation and convection for cool stars from main sequence to red giant stages of evolution.

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“…PanSTARRS detects a very blue object at a projected separation of ∼4″ and PA of ∼300°. It is unassociated according to Gaia DR2 measurements and cataloged as a white dwarf by Bai et al (2018). This blue object is too faint for both the visible and infrared Robo-AO cameras.…”

Section: Substellar Candidatesmentioning

confidence: 94%

Large Adaptive Optics Survey for Substellar Objects around Young, Nearby, Low-mass Stars with Robo-AO

Salama

Baranec

et al. 2021

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We present results from the Large Adaptive optics Survey for Substellar Objects, where the goal is to directly image new substellar companions (<70 M Jup ) at wide orbital separations (50 au) around young (300 Myr), nearby (<100 pc), low-mass (≈0.1-0.8 M  ) stars. We report on 427 young stars imaged in the visible (i′) and nearinfrared (J or H ) simultaneously with Robo-AO on the Kitt Peak 2.1 m telescope and later the Maunakea University of Hawaii 2.2 m telescope. To undertake the observations, we commissioned a new infrared camera for Robo-AO that uses a low-noise high-speed SAPHIRA avalanche photodiode detector. We detected 121 companion candidates around 111 stars, of which 62 companions are physically associated based on Gaia DR2 parallaxes and proper motions, another 45 require follow-up observations to confirm physical association, and 14 are background objects. The companion separations range from 2 to 1101 au and reach contrast ratios of 7.7 mag in the nearinfrared compared to the primary. The majority of confirmed and pending candidates are stellar companions, with ∼5 being potentially substellar and requiring follow-up observations for confirmation. We also detected a 43±9 M Jup and an 81±5 M Jup companion that were previously reported. We found 34 of our targets have acceleration measurements detected using Hipparcos-Gaia proper motions. Of those, -+ 58 1412 % of the 12 stars with imaged companion candidates have significant accelerations (c > 11.8 2), while only -+ 23 6 11 % of the remaining 22 stars with no detected companion have significant accelerations. The significance of the acceleration decreases with increasing companion separation. These young accelerating low-mass stars with companions will eventually yield dynamical masses with future orbit monitoring.

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The UV Emission of Stars in the LAMOST Survey. I. Catalogs

Cited by 25 publications

References 64 publications

New mercury-manganese stars and candidates from LAMOST DR4

New mercury-manganese stars and candidates from LAMOST DR4

Rotationally Driven Ultraviolet Emission of Red Giant Stars

Large Adaptive Optics Survey for Substellar Objects around Young, Nearby, Low-mass Stars with Robo-AO

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