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

2019 ◽  
Vol 489 (4) ◽  
pp. 5146-5164 ◽  
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.

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

2020 ◽  
Vol 633 ◽  
pp. A28 ◽  
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.

scholarly journals First discovery of an ultra-cool white dwarf benchmark in common proper motion with an M dwarf

2020 ◽  
Vol 493 (4) ◽  
pp. 6001-6010
Author(s):  
M C Lam ◽  
N C Hambly ◽  
N Lodieu ◽  
S Blouin ◽  
E J Harvey ◽  
...  
Keyword(s):  
White Dwarf ◽  
Proper Motion ◽  
Main Sequence ◽  
Gravitational Settling ◽  
Spatial Velocity ◽  
Effective Temperatures ◽  
Cool White Dwarfs ◽  
M Dwarf ◽  
The Universe

ABSTRACT Ultra-cool white dwarfs are among the oldest stellar remnants in the Universe. Their efficient gravitational settling and low effective temperatures are responsible for the smooth spectra they exhibit. For that reason, it is not possible to derive their radial velocities or to find the chemistry of the progenitors. The best that can be done is to infer such properties from associated sources, which are coeval. The simplest form of such a system is a common proper motion pair where one star is an evolved degenerate and the other a main-sequence star. In this work, we present the discovery of the first of such a system, the M dwarf LHS 6328 and the ultra-cool white dwarf PSO J1801+625, from the Pan-STARRS 1 3π survey and the Gaia Data Release 2. Follow-up spectra were collected covering a usable wavelength range of 3750–24 500 Å. Their spectra show that the white dwarf has an effective temperature of 3550 K and surface gravity of log g = 7.45 ± 0.13 or log g = 7.49 ± 0.13 for a CO or He core, respectively, when compared against synthetic spectra of ultra-cool white dwarf atmosphere models. The system has slightly subsolar metallicity with −0.25 < [Fe/H] < 0.0, and a spatial velocity of (U, V, W) = (−114.26 ± 0.24, 222.94 ± 0.60, 10.25 ± 0.34) km s−1, the first radial velocity and metallicity measurements of an ultra-cool white dwarf. This makes it the first and only benchmark of its kind to date.

scholarly journals HST-FGS Astrometry of the Low Mass Binary L722-22

1999 ◽  
Vol 172 ◽  
pp. 405-407
Author(s):  
L.G. Taff ◽  
John L. Hershey
Keyword(s):  
Main Sequence ◽  
Hubble Space Telescope ◽  
Brown Dwarf ◽  
One Dimensional ◽  
Photographic Images ◽  
System A ◽  
Data Points ◽  
Low Mass ◽  
The Masses ◽  
M Dwarf

The M dwarf L722-22 (= LHS 1047) was discovered to be a binary system by Ianna 20 years ago. The analysis of the ground- based data indicated a mass 0.06M⊙ for the secondary. This is below the nominal stellar mass limit of 0.08M⊙. The importance of potential “brown-dwarf” candidates, and the fact that the masses of both components place them near the end of the main sequence, made this system a prime object for further, intensive, study.This close (separation 0."3), faint (V = 11.m5, 14.m4) binary was near the limit for ground-based work. The residuals of an individual night’s photographic data were typically at the 50% level. Also, the photographic images are completely blended. The few one-dimensional speckle data points yielded a merged, asymmetric image profile. Finally, this system is too faint for HIPPARCOS. Our proposal for Hubble Space Telescope Fine Guidance Sensor (FGS) observing was approved in 1992.

scholarly journals Lithium in Giants

1995 ◽  
Vol 10 ◽  
pp. 449-450
Author(s):  
Suchitra Balachandran
Keyword(s):  
Main Sequence ◽  
Standard Model Prediction ◽  
Stellar Model ◽  
High Mass ◽  
Lithium Abundance ◽  
Convective Envelope ◽  
The Standard Model ◽  
Turbulence Mixing ◽  
Surface Convection

In the standard stellar model, lithium burning does not occur during the first-ascent giant branch phase. The surface lithium abundance in a first-ascent or clump giant is thus the product of the lithium abundance of its main sequence progenitor and subsequent dilution by the deepening convective envelope. Iben’s (1967a, b) early calculations predicted that the dilution factor would vary between a factor of about 28 in a 1 M⊙ star to a factor of 60 in a 5 M⊙ star. More recent calculations with improved physics show remarkably little change in these predicted dilution factors (Pinson-neault, pvt. comm.). Since Li only survives in the outer 2-3 % by mass of a main sequence star, the maximum redgiant ∼ abundance is predicted to be ∼ log e(Li)=1.5 to within a factor of two. Even lower abundances will result if surface Li is destroyed during the main sequence phase. Lithium depletion on the main sequence has been well documented in stars of spectral type mid-F and later and have been explained by a variety of non-standard mechanisms (e.g., rotation, diffusion and turbulence). Mixing induced by such mechanisms is not expected in high-mass stars (M⊙ > 1.5) which have insignificant surface convection. Yet recent observations reveal that non-standard processes may be at work in these stars as well.Lithium abundances far below the predicted maximum value are seen in high-mass cluster giants, and in some clusters large spreads in Li are observed in giants of roughly the same mass (Gilroy 1989). If, in concordance with the standard-model prediction, one assumes that Li burning on the giant branch is unlikely, then both the destruction and the scatter of Li must be accounted for on the main sequence. Since the surface convection zones are insignificant, other forms of Li-loss (e.g. mass loss, meridional circulation) may have to be resorted to. Unfortunately the main sequence progenitors of most of these giants are too hot to have a measurable Li I feature, but observations of field late-A stars by Burkhart and Coupry (1991) reveal some evidence for surface Li-loss. Follow-up observations of Li inclusters, and Be and B abundance determinations would be useful. Lithium burning on the giant branch should be investigated theoretically.

scholarly journals Workshop on Stellar Tidal Disruption

2011 ◽  
Vol 7 (S285) ◽  
pp. 261-268
Author(s):  
Glennys R. Farrar
Keyword(s):  
Accretion Disks ◽  
Main Sequence ◽  
Light Curves ◽  
Late Time ◽  
Tidal Disruption ◽  
X Ray ◽  
Spectral Signatures ◽  
The Past ◽  
Observational Status

AbstractThe past year has seen major advances in the observational status of Stellar Tidal Disruption, with the discovery of two strong optical candidates in archived SDSS data and the real-time X-ray detection of Swift J1644+57, plus rapid radio and optical follow-up establishing it as a probable Tidal Disruption Flare (TDF) in “blazar mode”. These observations motivated a workshop devoted to discussion of such events and of the theory of their emission and flare rate. Observational contributions included a presentation of Swift J2058+05 (a possible second example of a TDF in blazar mode), reports on the late-time evolution and X-ray variability of the two Swift events, and a proposal that additional candidates may be evidenced by spectral signatures in SDSS. Theory presentations included models of radio emission, theory of light curves and the proposal that GRB101225A may be the Galactic tidal disruption of a neutron star, an interpretation of Swift J1644+57 as due to the disruption of a white dwarf instead of main-sequence star, calculation of the dependence of the TDF rate on the spin of the black hole, and analysis of the SDSS events, fitting their SEDs to profiles of thoretical emission from accretion disks and showing that their luminosity and rate are consistent with the proposal that TDEs can be responsible for UHECR acceleration.

scholarly journals Multiwavelength Photometry of the Young Intermediate Mass Eclipsing Binary TY CrA

2011 ◽  
Vol 7 (S282) ◽  
pp. 59-60
Author(s):  
M. Ammler-von Eiff ◽  
M. Vaňko ◽  
T. Pribulla ◽  
E. Covino ◽  
R. Neuhäuser ◽  
...  
Keyword(s):  
Main Sequence ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
High Mass ◽  
Intermediate Mass ◽  
Eclipsing Binary ◽  
Orbital Parameters ◽  
Optical Wavelength ◽  
Near Ir ◽  
Ir Bands

AbstractOne of the handful of known PMS eclipsing binaries is a component of the spectroscopic triple TY CrA. Its secondary component is particularly interesting since it is a star of relatively high mass (1.64 M⊙) which is still on the pre-main sequence. The eclipsing binary was analyzed in the optical wavelength range ~10 years ago, however, the crucial secondary eclipse minimum is very shallow. Therefore, we are obtaining new photometry in both optical and near-IR bands. We present first observations in (BVRI) which show that the secondary eclipse depth increases to about 0.1 mag in the I band. The increased eclipse depth with respect to other bands will help to better determine the colours and dimensions of the system. Furthermore, we show and discuss first near-IR observations of the primary eclipse. In addition to the light curves we are obtaining radial velocities in order to pin down the orbital parameters of the triple. Our first observations agree with the orbital parameters derived ~10 years ago.

scholarly journals Finding orbital motion of sub-stellar companions - the case of TWA 5B

2007 ◽  
Vol 3 (S248) ◽  
pp. 126-127 ◽  
Author(s):  
T. Schmidt ◽  
R. Neuhäuser ◽  
M. Mugrauer
Keyword(s):  
Proper Motion ◽  
Main Sequence ◽  
Orbital Motion ◽  
T Tauri Stars ◽  
Brown Dwarf ◽  
T Tauri ◽  
Combining Data ◽  
Tw Hydrae Association ◽  
Astrometric Data ◽  
Triple Star

AbstractTWA 5B is a brown dwarf companion of H=12 mag, 2″ off the ~5 mag brighter triple star CoD-33° 7795 (=TWA 5), a member of the TW Hydrae association of T Tauri stars at ~55 pc. This object is the first brown dwarf around a pre-main-sequence star (confirmed by common proper motion) ever found. In the last year we have newly reduced VLT NaCo data originally taken in 2003 and combined it with all the available astrometric data of the system to investigate possibly detectable orbital motion of the system. Indeed we were able to find linear orbital motion of the system combining data from HST, VLT and Gemini-North.

scholarly journals The nature of giant clumps in high-z discs: a deep-learning comparison of simulations and observations

2020 ◽  
Vol 501 (1) ◽  
pp. 730-746
Author(s):  
Omri Ginzburg ◽  
Marc Huertas-Company ◽  
Avishai Dekel ◽  
Nir Mandelker ◽  
Gregory Snyder ◽  
...  
Keyword(s):  
Neural Network ◽  
Deep Learning ◽  
Main Sequence ◽  
High Redshift ◽  
High Mass ◽  
Galactic Centre ◽  
Preferential Formation ◽  
Maximum Resolution ◽  
Supernova Feedback ◽  
Disc Galaxies

ABSTRACT We use deep learning to explore the nature of observed giant clumps in high-redshift disc galaxies, based on their identification and classification in cosmological simulations. Simulated clumps are detected using the 3D gas and stellar densities in the VELA zoom-in cosmological simulation suite, with ${\sim}25\ \rm {pc}$ maximum resolution, targeting main-sequence galaxies at 1 < z < 3. The clumps are classified as long-lived clumps (LLCs) or short-lived clumps (SLCs) based on their longevity in the simulations. We then train neural networks to detect and classify the simulated clumps in mock, multicolour, dusty, and noisy HST-like images. The clumps are detected using an encoder–decoder convolutional neural network (CNN), and are classified according to their longevity using a vanilla CNN. Tests using the simulations show our detector and classifier to be ${\sim}80{{\ \rm per\ cent}}$ complete and ${\sim}80{{\ \rm per\ cent}}$ pure for clumps more massive than ∼107.5 M⊙. When applied to observed galaxies in the CANDELS/GOODS S+N fields, we find both types of clumps to appear in similar abundances in the simulations and the observations. LLCs are, on average, more massive than SLCs by ∼0.5 dex, and they dominate the clump population above Mc ≳ 107.6 M⊙. LLCs tend to be found closer to the galactic centre, indicating clump migration to the centre or preferential formation at smaller radii. The LLCs are found to reside in high-mass galaxies, indicating better clump survivability under supernova feedback there, due to clumps being more massive in these galaxies. We find the clump masses and radial positions in the simulations and the observations to agree within a factor of 2.

scholarly journals SuperWASP variable stars: classifying light curves using citizen science

2021 ◽  
Vol 502 (1) ◽  
pp. 1299-1311
Author(s):  
Heidi B Thiemann ◽  
Andrew J Norton ◽  
Hugh J Dickinson ◽  
Adam McMaster ◽  
Ulrich C Kolb
Keyword(s):  
Variable Stars ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
Data Set ◽  
Resultant Data ◽  
Sky Survey ◽  
Short Period ◽  
Contact Binaries ◽  
Analysis Of Results

ABSTRACT We present the first analysis of results from the SuperWASP variable stars Zooniverse project, which is aiming to classify 1.6 million phase-folded light curves of candidate stellar variables observed by the SuperWASP all sky survey with periods detected in the SuperWASP periodicity catalogue. The resultant data set currently contains >1 million classifications corresponding to >500 000 object–period combinations, provided by citizen–scientist volunteers. Volunteer-classified light curves have ∼89 per cent accuracy for detached and semidetached eclipsing binaries, but only ∼9 per cent accuracy for rotationally modulated variables, based on known objects. We demonstrate that this Zooniverse project will be valuable for both population studies of individual variable types and the identification of stellar variables for follow-up. We present preliminary findings on various unique and extreme variables in this analysis, including long-period contact binaries and binaries near the short-period cut-off, and we identify 301 previously unknown binaries and pulsators. We are now in the process of developing a web portal to enable other researchers to access the outputs of the SuperWASP variable stars project.

scholarly journals Intermittent maser flare around the high-mass young stellar object G353.273+0.641

2012 ◽  
Vol 8 (S287) ◽  
pp. 98-102
Author(s):  
Kazuhito Motogi ◽  
Kazuo Sorai ◽  
Kenta Fujisawa ◽  
Koichiro Sugiyama ◽  
Mareki Honma
Keyword(s):  
Light Curve ◽  
Small Area ◽  
Linear Acceleration ◽  
High Mass ◽  
Velocity Range ◽  
Time Resolved ◽  
Almost All ◽  
Maser Sources ◽  
Water Maser

AbstractThe water maser site associated with G353.273+0.641 is classified as a dominant blueshifted H2O maser, which shows an extremely wide velocity range (± 100 km s−1) with almost all flux concentrated in the highly blueshifted emission. The previous study has proposed that this peculiar H2O maser site is excited by a pole-on jet from high mass protostellar object. We report on the monitoring of 22-GHz H2O maser emission from G353.273+0.641 with the VLBI Exploration of Radio Astrometry (VERA) and the Tomakamai 11-m radio telescope. Our VLBI imaging has shown that all maser features are distributed within a very small area of 200 × 200 au2, in spite of the wide velocity range (> 100 km s−1). The light curve obtained by weekly single-dish monitoring shows notably intermittent variation. We have detected three maser flares during three years. Frequent VLBI monitoring has revealed that these flare activities have been accompanied by a significant change of the maser alignments. We have also detected synchronized linear acceleration (−5 km s−1yr−1) of two isolated velocity components, suggesting a lower-limit momentum rate of 10−3 M⊙ km s−1yr−1 for the maser acceleration. All our results support the previously proposed pole-on jet scenario, and finally, a radio jet itself has been detected in our follow-up ATCA observation. If highly intermittent maser flares directly reflect episodic jet-launchings, G353.273+0.641 and similar dominant blueshifted water maser sources can be suitable targets for a time-resolved study of high mass protostellar jet.

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