EDEN: Flare Activity of the Nearby Exoplanet-hosting M Dwarf Wolf 359 Based on K2 and EDEN Light Curves

We study the short-time evolutionary history of the well-known contact binary VW Cep. Our analysis is based partly on the numerous UBV lightcurves obtained at Tartu Observatory, IUE spectra, and samples from the published data. Special attention is given to the effects of asymmetry of the light curves. A higher degree of asymmetry outside the eclipses along with the significant displacements of the brightness maxima in respect to the elongation phase is interpreted as evidence that a considerable portion of the flaring source is concentrated close to the neck connecting the components. We discuss the nature of asymmetry in terms of possible mass exchange and the flare activity and compare the results of our model computations with the record of orbital period variations over the last 60 years.

Download Full-text

Simulations of starspot anomalies within TESS exoplanetary transit light curves

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935742 ◽

2019 ◽

Vol 630 ◽

pp. A114 ◽

Cited By ~ 1

Author(s):

J. Tregloan-Reed ◽

E. Unda-Sanzana

Keyword(s):

Light Curve ◽

Detection Limits ◽

Mean Amplitude ◽

Light Curves ◽

Dwarf Stars ◽

Spotted Stars ◽

M Dwarf Stars ◽

M Dwarf ◽

The Relationship ◽

Host Stars

Context. The primary targets of the NASA Transiting Exoplanet Survey Satellite (TESS) are K and M dwarf stars within our solar neighbourhood. Young K and M dwarf stars are known to exhibit a high starspot coverage (≈50%), however, older stars are known to show fewer starspots. This implies that TESS transit light curves at 2 min cadence may contain starspot anomalies, and if so, will require transit-starspot models to determine accurately the properties of the system. Aims. The goals are to determine if starspot anomalies can manifest in TESS transit light curves, to determine the detection limits of the starspot anomalies, and to examine the relationship between the change in flux caused by the starspot anomaly and the planetary transit. Methods. We conducted 20 573 simulations of planetary transits around spotted stars using the transit-starspot model, PRISM. In total 3888 different scenarios were considered using three different host star spectral types, M4V, M1V, and K5V. The mean amplitude of the starspot anomaly was measured and compared to the photometric precision of the light curve to determine if the characteristic “blip” of the starspot anomaly was noticeable in the light curve. Results. The simulations show that starspot anomalies are observable in TESS 2 min cadence data. The smallest starspot detectable in TESS transit light curves has a radius of ≈ 1900 km. The starspot detection limits for the three host stars are 4900 ± 1700 km (M4V), 13 800 ± 6000 km (M1V), and 15 900 ± 6800 km (K5V). The smallest change in flux of the starspot (ΔFspot = 0.00015 ± 0.00001) can be detected when the ratio of planetary to stellar radii k = 0.082 ± 0.004. Conclusions. The results confirm known dependencies between the amplitude of the starspot anomaly and the photometric parameters of the light curve. The results facilitated the characterisation of the relationship between the change in flux of the starspot anomaly and the change in flux of the planetary transit for TESS transit light curves.

Download Full-text

MuSCAT2 multicolour validation of TESS candidates: an ultra-short-period substellar object around an M dwarf

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935958 ◽

2020 ◽

Vol 633 ◽

pp. A28 ◽

Cited By ~ 4

Author(s):

H. Parviainen ◽

E. Palle ◽

M. R. Zapatero-Osorio ◽

P. Montanes Rodriguez ◽

F. Murgas ◽

...

Keyword(s):

Radius Ratio ◽

Light Curves ◽

Reliable Estimate ◽

Brown Dwarf ◽

Colour Difference ◽

Stellar Radius ◽

Short Period ◽

Transit Model ◽

M Dwarf

Context. We report the discovery of TOI 263.01 (TIC 120916706), a transiting substellar object (R = 0.87 RJup) orbiting a faint M3.5 V dwarf (V = 18.97) on a 0.56 d orbit. Aims. We setout to determine the nature of the Transiting Exoplanet Survey Satellite (TESS) planet candidate TOI 263.01 using ground-based multicolour transit photometry. The host star is faint, which makes radial-velocity confirmation challenging, but the large transit depth makes the candidate suitable for validation through multicolour photometry. Methods. Our analysis combines three transits observed simultaneously in r′, i′, and zs bands usingthe MuSCAT2 multicolour imager, three LCOGT-observed transit light curves in g′, r′, and i′ bands, a TESS light curve from Sector 3, and a low-resolution spectrum for stellar characterisation observed with the ALFOSC spectrograph. We modelled the light curves with PYTRANSIT using a transit model that includes a physics-based light contamination component, allowing us to estimate the contamination from unresolved sources from the multicolour photometry. Using this information we were able to derive the true planet–star radius ratio marginalised over the contamination allowed by the photometry.Combining this with the stellar radius, we were able to make a reliable estimate of the absolute radius of the object. Results. The ground-based photometry strongly excludes contamination from unresolved sources with a significant colour difference to TOI 263. Furthermore, contamination from sources of the same stellar type as the host is constrained to levels where the true radius ratio posterior has a median of 0.217 and a 99 percentile of0.286. The median and maximum radius ratios correspond to absolute planet radii of 0.87 and 1.41 RJup, respectively,which confirms the substellar nature of the planet candidate. The object is either a giant planetor a brown dwarf (BD) located deep inside the so-called “brown dwarf desert”. Both possibilities offer a challenge to current planet/BD formation models and make TOI 263.01 an object that merits in-depth follow-up studies.

Download Full-text

Unsupervised machine learning for transient discovery in deeper, wider, faster light curves

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2395 ◽

2020 ◽

Vol 498 (3) ◽

pp. 3077-3094

Author(s):

Sara Webb ◽

Michelle Lochner ◽

Daniel Muthukrishna ◽

Jeff Cooke ◽

Chris Flynn ◽

...

Keyword(s):

Anomaly Detection ◽

Detection Algorithm ◽

Light Curves ◽

Wide Field ◽

Proof Of Concept ◽

Stellar Flare ◽

Field Surveys ◽

Clustering Technique ◽

M Dwarf ◽

Visual Interface

ABSTRACT Identification of anomalous light curves within time-domain surveys is often challenging. In addition, with the growing number of wide-field surveys and the volume of data produced exceeding astronomers’ ability for manual evaluation, outlier and anomaly detection is becoming vital for transient science. We present an unsupervised method for transient discovery using a clustering technique and the astronomaly package. As proof of concept, we evaluate 85 553 min-cadenced light curves collected over two ∼1.5 h periods as part of the Deeper, Wider, Faster program, using two different telescope dithering strategies. By combining the clustering technique HDBSCAN with the isolation forest anomaly detection algorithm via the visual interface of astronomaly, we are able to rapidly isolate anomalous sources for further analysis. We successfully recover the known variable sources, across a range of catalogues from within the fields, and find a further seven uncatalogued variables and two stellar flare events, including a rarely observed ultrafast flare (∼5 min) from a likely M-dwarf.

Download Full-text

M-dwarf Eclipsing Binaries with Flare Activity

The Astrophysical Journal ◽

10.3847/1538-4357/ab774a ◽

2020 ◽

Vol 892 (1) ◽

pp. 58

Author(s):

L.-C. Huang ◽

W.-H. Ip ◽

C.-L. Lin ◽

X.-L. Zhang ◽

Y.-H. Song ◽

...

Keyword(s):

Eclipsing Binaries ◽

Flare Activity ◽

M Dwarf

Download Full-text

NGTS-7Ab: an ultrashort-period brown dwarf transiting a tidally locked and active M dwarf

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2496 ◽

2019 ◽

Vol 489 (4) ◽

pp. 5146-5164 ◽

Cited By ~ 15

Author(s):

James A G Jackman ◽

Peter J Wheatley ◽

Dan Bayliss ◽

Samuel Gill ◽

Simon T Hodgkin ◽

...

Keyword(s):

Proper Motion ◽

Main Sequence ◽

Light Curves ◽

High Mass ◽

Spin Orbit ◽

Brown Dwarf ◽

Systemic Velocity ◽

Magnetic Braking ◽

M Dwarf

ABSTRACT We present the discovery of NGTS-7Ab, a high-mass brown dwarf transiting an M dwarf with a period of 16.2 h, discovered as part of the Next Generation Transit Survey (NGTS). This is the shortest period transiting brown dwarf around a main or pre-main sequence star to date. The M star host (NGTS-7A) has an age of roughly 55 Myr and is in a state of spin–orbit synchronization, which we attribute to tidal interaction with the brown dwarf acting to spin-up the star. The host star is magnetically active and shows multiple flares across the NGTS and follow-up light curves, which we use to probe the flare–star-spot phase relation. The host star also has an M star companion at a separation of 1.13 arcsec with very similar proper motion and systemic velocity, suggesting that the NGTS-7 system is a hierarchical triple. The combination of tidal synchronisation and magnetic braking is expected to drive on-going decay of the brown dwarf orbit, with a remaining lifetime of only 5–10 Myr.

Download Full-text

Fast photometric variability of very low mass stars in IC 348: detection of superflare in an M dwarf

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3574 ◽

2020 ◽

Vol 500 (4) ◽

pp. 5106-5116

Author(s):

Samrat Ghosh ◽

Soumen Mondal ◽

Somnath Dutta ◽

Ramkrishna Das ◽

Santosh Joshi ◽

...

Keyword(s):

Light Curves ◽

M Dwarfs ◽

Low Mass Stars ◽

Period Range ◽

Photometric Variability ◽

Star Forming ◽

Low Mass ◽

M Dwarf ◽

Variability Study ◽

Optical Flare

ABSTRACT We present here optical I-band photometric variability study down to ≃19 mag of a young (∼2–3 Myr) star-forming region IC 348 in the Perseus molecular cloud. We aim to explore the fast rotation (in the time-scales of hours) in very low-mass stars including brown dwarfs (BDs). From a sample of 177 light curves using our new I-band observations, we detect new photometric variability in 22 young M dwarfs including 6 BDs, which are bonafide members in IC 348 and well characterized in the spectral type of M dwarfs. Out of 22 variables, 11 M dwarfs including one BD show hour-scale periodic variability in the period range 3.5–11 h and rest are aperiodic in nature. Interestingly, an optical flare is detected in a young M2.75 dwarf in one night data on 2016 December 20. From the flare light curve, we estimate the emitted flared energy of 1.48 × 1035 erg. The observed flared energy with an uncertainty of tens of per cent is close to the superflare range (∼1034 erg), which is rarely observed in active M dwarfs.

Download Full-text

High-resolution spectroscopy of flares and CMEs on AD Leonis

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936904 ◽

2020 ◽

Vol 637 ◽

pp. A13 ◽

Cited By ~ 4

Author(s):

P. Muheki ◽

E. W. Guenther ◽

T. Mutabazi ◽

E. Jurua

Keyword(s):

High Resolution ◽

Spectral Lines ◽

High Resolution Spectroscopy ◽

Flare Activity ◽

The Sun ◽

M Dwarfs ◽

Highly Active ◽

M Stars ◽

High Level ◽

M Dwarf

Context. Flares and coronal mass ejections (CMEs) are important for the evolution of the atmospheres of planets and their potential habitability, particularly for planets orbiting M stars at a distance <0.4 AU. Detections of CMEs on these stars have been sparse, and previous studies have therefore modelled their occurrence frequency by scaling up solar relations. However, because the topology and strength of the magnetic fields on M stars is different from that of the Sun, it is not obvious that this approach works well. Aims. We used a large number of high-resolution spectra to study flares, CMEs, and their dynamics of the active M dwarf star AD Leo. The results can then be used as reference for other M dwarfs. Methods. We obtained more than 2000 high-resolution spectra (R ~ 35 000) of the highly active M dwarf AD Leo, which is viewed nearly pole on. Using these data, we studied the behaviour of the spectral lines Hα, Hβ, and He I 5876 in detail and investigated asymmetric features that might be Doppler signatures of CMEs. Results. We detected numerous flares. The largest flare emitted 8.32 × 1031 erg in Hβ and 2.12 × 1032 erg in Hα. Although the spectral lines in this and other events showed a significant blue asymmetry, the velocities associated with it are far below the escape velocity. Conclusions. Although AD Leo shows a high level of flare activity, the number of CMEs is relatively low. It is thus not appropriate to use the same flare-to-CME relation for M dwarfs as for the Sun.

Download Full-text

The shape of M dwarf flares in Kepler light curves

Proceedings of the International Astronomical Union ◽

10.1017/s174392131600867x ◽

2015 ◽

Vol 11 (S320) ◽

pp. 128-133

Author(s):

James R. A. Davenport

Keyword(s):

White Light ◽

Statistical Properties ◽

Light Curves ◽

High Fidelity ◽

Single Star ◽

Initial Rise ◽

Stellar Flares ◽

Complex Events ◽

Solar Events ◽

M Dwarf

AbstractUltra-precise light curves from Kepler provide the best opportunity to determine rates and statistical properties of stellar flares. From 11 months of data on the active M4 dwarf, GJ 1243, we have built the largest catalog of flares for a single star: over 6100 events. Combining 885 of our most pristine flares, we generated an empirical white-light flare template. This high-fidelity template shows a rapid initial rise, and two distinct exponential cooling phases. This template is useful in constraining flare energies and for improved flare detection in many surveys. Complex, multi-peaked events are more common for higher energy flares in this sample. Using our flare template we characterize the structure of complex events. In this contributed talk, I presented results from our boutique study of GJ 1243, and described an expanded investigation of the structure of complex flares and their connection to solar events.

Download Full-text

Flare Activity in the NGC 1275 Nucleus

Symposium - International Astronomical Union ◽

10.1017/s0074180900233391 ◽

1996 ◽

Vol 171 ◽

pp. 420-420 ◽

Cited By ~ 1

Author(s):

N.I. Merkulova ◽

L.P. Metik

Keyword(s):

Light Curve ◽

Seyfert Galaxies ◽

Crimean Astrophysical Observatory ◽

Light Curves ◽

Flare Activity ◽

Different Types ◽

Ngc 1275 ◽

First Time

The simultaneous UBVRI – observations of some Seyfert galaxies have been carried out at Crimean Astrophysical Observatory using the 1.25m telescope. Photometric errors are less than 0.01 mag. By analysis of the NGC 1275 light curves within one night we are discovered at least two types of variability: 1) The flares with the maximal amplitudes of 5 – 30 % in the U-band and durations of 15 – 30 minutes. 2) For the first time we have found rapid red flares. For instance, the red flare on the light curve 22-23.10.1992 lasted ∼ 65 minutes (see Figure. Vertical axes are in magnitudes). The amplitude in the filter I is ∼ 25 % (top panel). The light curve in the U-band is on the bottom panel. Fluxes in the U,B,V-bands were almost constant. One can see the flux decreasing in some filters before this flare. We conclude, that light curve of NGC 1275 nucleus could be represented by a superposition of rapid flares of different types.

Download Full-text