Ultracool dwarfs identified using spectra in LAMOST DR7

Wang, Y.-F.; Luo, A-Li; Chen, W.-P.; Jones, H. R. A.; Du, Bing; Li, Y.-B.; Zhang, S.; Bai, Zhong-Rui; Kong, Xiao; Guo, Yanxin

doi:10.1051/0004-6361/202142009

Cited by 9 publications

(2 citation statements)

References 62 publications

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“…First, we searched for binaries and pulsating variables using the light curves. We conducted a list of variable stars from various surveys, including Kepler (e.g., McQuillan et al 2013McQuillan et al , 2014Kirk et al 2016;Santos et al 2019), K2 (Reinhold & Hekker 2020), ZTF (Chen et al 2020), ASAS-SN (e.g., Jayasinghe et al 2020;Christy et al 2023), Catalina (Drake et al 2014), WISE (Chen et al 2018), Gaia (Rimoldini et al 2023), TESS (e.g., Howard et al 2022;Prsa et al 2022), GCVS (Samus et al 2009), OGLE (Soszyński et al 2016), LAMOST DR7 (Wang et al 2022), MEarth (Newton et al 2016), and HATNet (Hartman et al 2011). We cross-matched our sample with these variable catalogs using a matching radius of 3″.…”

Section: Binaries and Pulsating Variablesmentioning

confidence: 99%

Ultraviolet and Chromospheric Activity and Habitability of M Stars

Li,

Wang,

Han

et al. 2024

ApJ

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M-type stars are crucial for stellar activity studies because they cover two types of magnetic dynamos and are particularly intriguing for habitability studies due to their abundance and long lifespans during the main-sequence stage. In this paper, we used the LAMOST DR9 catalog and the GALEX UV archive data to investigate the chromospheric and UV activities of M-type stars. All the chromospheric and UV activity indices clearly show that the saturated and unsaturated regimes, and the well-known activity–rotation relation, are consistent with previous studies. Both the FUV and NUV activity indices exhibit a single-peaked distribution, while the Hα and Ca ii H&K indices show a distinct double-peaked distribution. The gap between these peaks suggests a rapid transition from a saturated population to an unsaturated one. The smoothly varying distributions of different subtypes suggest a rotation-dependent dynamo for both early-type (partly convective) to late-type (fully convective) M stars. We identified a group of stars with high UV activity above the saturation regime (log R NUV ′ > − 2.5 ) but low chromospheric activity, and the underlying reason is unknown. By calculating the continuously habitable zone and the UV habitable zone for each star, we found that about 70% stars in the total sample and 40% stars within 100 pc are located in the overlapping region of these two habitable zones, indicating that a number of M stars are potentially habitable. Finally, we examined the possibility of UV activity studies of M stars using the China Space Station Telescope.

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Section: Binaries and Pulsating Variablesmentioning

confidence: 99%

Ultraviolet and Chromospheric Activity and Habitability of M Stars

Li,

Wang,

Han

et al. 2024

ApJ

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“…The Ground-based Wide Angle Camera (GWAC), located at the Xinglong Observatory of National Astronomical Observatories, Chinese Academy of Sciences, is an array of telescopes with wide-angle cameras dedicated to optical transient survey (Wei et al 2016). It monitors the sky with a cadence of 15 s (i.e., 10 s for exposure and 5 s for readout), aiming to detect shortduration transients such as gamma-ray bursts (Xin et al 2023a), stellar flares (Wang et al 2021(Wang et al , 2022Li et al 2023), the optical counterpart of gravitational waves (Turpin et al 2020), and fast radio bursts (Xin et al 2021a). Currently, the GWAC is composed of four units.…”

Section: The Observational Facilitymentioning

confidence: 99%

White-light Superflare and Long-term Activity of the Nearby M7-type Binary EI Cnc Observed with GWAC System

Li,

Wang,

Xin

et al. 2023

ApJ

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Stellar white-light flares are believed to play an essential role in the physical and chemical properties of the atmosphere of the surrounding exoplanets. Here we report an optical monitoring campaign on the nearby flaring system EI Cnc carried out by the Ground-based Wide Angle Camera (GWAC) and its dedicated follow-up telescope. A superflare, coming from the brighter component EI CncA, was detected and observed, in which four components are required to properly model the complex decay light curve. The lower limit of flare energy in the R − band is estimated to be 3.3 × 1032 erg. A total of 27 flares are additionally detected from the GWAC archive data with a total duration of 290 hr. The inferred cumulative flare frequency distribution follows a quite shallow power-law function with a slope of β = − 0.50 ± 0.03 over the energy range between 1030 and 1033 erg, which reinforces the trend that stars cooler than M4 show enhanced superflare activity. The flares identified in EI Cnc enable us to extend the τ–E relationship previously established in the white-light superflares of solar-type stars down to an energy as low as ∼1030erg (i.e., by 3 orders): τ ∝ E 0.42±0.02, which suggests a common flare mechanism for stars with a type from M to solar-like and implies an invariant of B 1/3 υ A in the white-light flares.

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Radio emission as a stellar activity indicator

Yiu,

Vedantham,

Callingham

et al. 2024

A&A

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Radio observations of stars trace the plasma conditions and magnetic field properties of stellar magnetospheres and coronae. Depending on the plasma conditions at the emitter site, radio emission in the metre- and decimetre-wave bands is generated via different mechanisms, such as gyrosynchrotron, electron cyclotron maser instability, and plasma radiation processes. The ongoing LOFAR Two-metre Sky Survey (LoTSS) and VLA Sky Survey (VLASS) are currently the most sensitive wide-field radio sky surveys ever conducted. Because these surveys are untargeted, they provide an opportunity to study the statistical properties of the radio-emitting stellar population in an unbiased manner. Here we perform an untargeted search for stellar radio sources down to sub-mJy level using these radio surveys. We find that the population of radio-emitting stellar systems is mainly composed of two distinct categories: chromospherically active stellar (CAS) systems and M dwarfs. We also seek to identify signatures of a gradual transition within the M-dwarf population, from chromospheric or coronal acceleration close to the stellar surface similar to that observed on the Sun to magnetospheric acceleration occurring far from the stellar surface similar to that observed on Jupiter. We determine that radio detectability evolves with spectral type, and we identify a transition in radio detectability around spectral type M4, where stars become fully convective. Furthermore, we compare the radio detectability versus spectra type with X-ray and optical flare (observed by TESS) incidence statistics. We find that the radio efficiency of X-ray and optical flares, which is the fraction of flare energy channelled into radio-emitting charges, increases with spectral type. These results motivate us to conjecture that the emergence of large-scale magnetic fields in CAS systems and later M dwarfs leads to an increase in radio efficiency.

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Ultracool dwarfs identified using spectra in LAMOST DR7

Cited by 9 publications

References 62 publications

Ultraviolet and Chromospheric Activity and Habitability of M Stars

Ultraviolet and Chromospheric Activity and Habitability of M Stars

White-light Superflare and Long-term Activity of the Nearby M7-type Binary EI Cnc Observed with GWAC System

Radio emission as a stellar activity indicator

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