scholarly journals NGTS 15b, 16b, 17b and 18b: four hot Jupiters from the Next Generation Transit Survey

2021 ◽  
Author(s):  
Rosanna H Tilbrook ◽  
Matthew R Burleigh ◽  
Jean C Costes ◽  
Samuel Gill ◽  
Louise Dyregaard Nielsen ◽  
...  
Keyword(s):  
Heavy Element ◽  
Main Sequence ◽  
Next Generation ◽  
Physical Processes ◽  
Main Sequence Stars ◽  
Latent Factors ◽  
Hot Jupiters ◽  
Short Period ◽  
Statistical Studies ◽  
Inflationary Models

Abstract We report the discovery of four new hot Jupiters with the Next Generation Transit Survey (NGTS). NGTS-15b, NGTS-16b, NGTS-17b, and NGTS-18b are short-period (P < 5d) planets orbiting G-type main sequence stars, with radii and masses between 1.10–1.30 RJ and 0.41–0.76 MJ. By considering the host star luminosities and the planets’ small orbital separations (0.039–0.052 AU), we find that all four hot Jupiters are highly irradiated and therefore occupy a region of parameter space in which planetary inflation mechanisms become effective. Comparison with statistical studies and a consideration of the planets’ high incident fluxes reveals that NGTS-16b, NGTS-17b, and NGTS-18b are indeed likely inflated, although some disparities arise upon analysis with current Bayesian inflationary models. However, the underlying relationships which govern radius inflation remain poorly understood. We postulate that the inclusion of additional hyperparameters to describe latent factors such as heavy element fraction, as well as the addition of an updated catalogue of hot Jupiters, would refine inflationary models, thus furthering our understanding of the physical processes which give rise to inflated planets.

scholarly journals LAMOST telescope reveals that Neptunian cousins of hot Jupiters are mostly single offspring of stars that are rich in heavy elements

2017 ◽  
Vol 115 (2) ◽  
pp. 266-271 ◽  
Author(s):  
Subo Dong ◽  
Ji-Wei Xie ◽  
Ji-Lin Zhou ◽  
Zheng Zheng ◽  
Ali Luo
Keyword(s):  
Main Sequence ◽  
The Other ◽  
Heavy Elements ◽  
Main Sequence Stars ◽  
Hot Jupiters ◽  
Transiting Planets ◽  
Short Period ◽  
Data Release ◽  
Order Of Magnitude ◽  
Solar Type

We discover a population of short-period, Neptune-size planets sharing key similarities with hot Jupiters: both populations are preferentially hosted by metal-rich stars, and both are preferentially found in Kepler systems with single-transiting planets. We use accurate Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release 4 (DR4) stellar parameters for main-sequence stars to study the distributions of short-period (1d<P<10d)Kepler planets as a function of host star metallicity. The radius distribution of planets around metal-rich stars is more “puffed up” compared with that around metal-poor hosts. In two period–radius regimes, planets preferentially reside around metal-rich stars, while there are hardly any planets around metal-poor stars. One is the well-known hot Jupiters, and the other one is a population of Neptune-size planets (2R⊕≲Rp≲6R⊕), dubbed “Hoptunes.” Also like hot Jupiters, Hoptunes occur more frequently in systems with single-transiting planets although the fraction of Hoptunes occurring in multiples is larger than that of hot Jupiters. About 1% of solar-type stars host Hoptunes, and the frequencies of Hoptunes and hot Jupiters increase with consistent trends as a function of [Fe/H]. In the planet radius distribution, hot Jupiters and Hoptunes are separated by a “valley” at approximately Saturn size (in the range of 6R⊕≲Rp≲10R⊕), and this “hot-Saturn valley” represents approximately an order-of-magnitude decrease in planet frequency compared with hot Jupiters and Hoptunes. The empirical “kinship” between Hoptunes and hot Jupiters suggests likely common processes (migration and/or formation) responsible for their existence.

scholarly journals NGTS clusters survey – II. White-light flares from the youngest stars in Orion

2020 ◽  
Vol 497 (1) ◽  
pp. 809-817 ◽  
Author(s):  
James A G Jackman ◽  
Peter J Wheatley ◽  
Jack S Acton ◽  
David R Anderson ◽  
Claudia Belardi ◽  
...  
Keyword(s):  
White Light ◽  
Main Sequence ◽  
High Energy ◽  
Occurrence Rate ◽  
Next Generation ◽  
Main Sequence Stars ◽  
M Stars ◽  
Flaring Stars

ABSTRACT We present the detection of high-energy white-light flares from pre-main-sequence stars associated with the Orion Complex, observed as part of the Next Generation Transit Survey (NGTS). With energies up to 5.2 × 1035 erg these flares are some of the most energetic white-light flare events seen to date. We have used the NGTS observations of flaring and non-flaring stars to measure the average flare occurrence rate for 4 Myr M0–M3 stars. We have also combined our results with those from previous studies to predict average rates for flares above 1 × 1035 erg for early M stars in nearby young associations.

scholarly journals A Spectroscopic and Photometric Survey for Pre-Main Sequence Binaries

2001 ◽  
Vol 200 ◽  
pp. 165-168 ◽  
Author(s):  
Eike W. Guenther ◽  
Viki Joergens ◽  
Ralph Neuhäuser ◽  
Guillermo Torres ◽  
Natalie Stout Batalha ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Main Sequence ◽  
Spectroscopic Binaries ◽  
Main Sequence Stars ◽  
Current State ◽  
Short Period ◽  
Velocity Variations ◽  
The Masses ◽  
Stellar Masses ◽  
Crucial Test

We give here an overview of the current state of our survey for pre-main sequence spectroscopic binaries. Up to now we have taken 739 spectra of 250 pre-main sequence stars. We find that 8% of the stars show significant radial velocity variations, and are thus most likely spectroscopic binaries. In addition to the targets showing radial velocity variations, 6% of the targets are double-lined spectroscopic binaries i.e., the total fraction of spectroscopic binaries is expected to be about 14%. All short-period SB2s are monitored photometrically in order to search for eclipses. An eclipsing SB2 would allow the direct measurement of the masses of both stellar components. Measurements of the stellar masses together with determinations of the stellar radii are a crucial test of evolutionary tracks of pre-main sequence stars.

scholarly journals Protoplanetary disks and hard X-rays

2009 ◽  
Vol 5 (H15) ◽  
pp. 744-744
Author(s):  
Eric D. Feigelson ◽  
Philip J. Armitage ◽  
Konstantin V. Getman
Keyword(s):  
Magnetic Reconnection ◽  
Main Sequence ◽  
Protoplanetary Disks ◽  
X Rays ◽  
Physical Processes ◽  
Main Sequence Stars ◽  
Magnetorotational Instability ◽  
X Ray ◽  
Neutral Gas ◽  
Ionization Fraction

The physics of protoplanetary disks and the early stages of planet formation is strongly affected by the level of ionization of the largely-neutral gas (Armitage 2009; Balbus 2009). Where the ionization fraction is above some limit around ~ 10−12, the magnetorotational instability (MRI) will ensue and the gas will become turbulent. The presence or absence of disk turbulence at various locations and times has profound implications for viscosity, accretion, dust settling, protoplanet migration and other physical processes. The dominant source of ionization is very likely X-rays from the host star (Glassgold et al. 2000). X-ray emission is elevated in all pre-main sequence stars primarily due to the magnetic reconnection flares similar to, but much more powerful and frequent than, flares on the surface of the contemporary Sun (Feigelson et al. 2007).

scholarly journals Lithium Abundance, Diffusion and Turbulence

1995 ◽  
Vol 10 ◽  
pp. 459-460
Author(s):  
G. Michaud ◽  
G. Beaudet
Keyword(s):  
Main Sequence ◽  
Normal Values ◽  
Present Theory ◽  
Constant Mass ◽  
Physical Processes ◽  
Main Sequence Stars ◽  
Hydrogen Burning ◽  
Lithium Abundance ◽  
Calculated Curve ◽  
Fully Coupled

Richer & Michaud (1993) calculated a series of envelopes fully coupled to non-rotating, constant mass, stellar evolution models of hydrogen burning stars with masses in the range of 1.2 to 2.2 M⊙, typical of A and F main sequence stars. They included He settling. The location of the theoretically predicted gap of the Hyades agrees quite well with the observed one, a result obtained without the introduction of any free parameter. At temperatures above the gap, while the observed lithium abundances are within a factor of 2-3 of normal values, the theoretical calculated curve drops to very low values. Diffusion velocities being fairly small, any other physical process with larger or similar velocities can reduce the effect of diffusion and produce the observed results. Mass loss is one such process. Another difficulty with the present theory is the width of the gap. Observations show that the observed gap is wider than the calculated one in the Hyades. This also suggests that other physical processes play an important role.

scholarly journals A Limit on the Space Density of Short-Period Binary White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 492-497
Author(s):  
Edward L. Robinson ◽  
Allen W. Shafter
Keyword(s):  
Orbital Period ◽  
Binary Stars ◽  
White Dwarfs ◽  
Main Sequence ◽  
Close Binaries ◽  
Main Sequence Stars ◽  
Space Density ◽  
Short Period ◽  
Hot Subdwarfs ◽  
Orbital Periods

We infer that detached binary white dwarfs with orbital periods of a few hours exist because we observe both their progenitors and their descendents. The binary LB 3459 has an orbital period of 6.3 hr and contains a pair of hot subdwarfs that will eventually cool to become white dwarfs (Kilkenny, Hill, and Penfold 1981). L870-2 is a pair of white dwarfs and, given enough time, its 1.55 d orbital period will decay to shorter periods (Saffer, Liebert, and Olszewski 1988). GP Com, AM CVn, V803 Cen, and PG1346+082 are interacting binary white dwarfs with orbital periods between 1051 s for AM CVn and 46.5 min for GP Com (Nather, Robinson, and Stover 1981; Solheim et al. 1984; Wood et al. 1987; O’Donoghue and Kilkenny 1988). These ultrashort period systems must be descendents of detached pairs of white dwarfs. We also expect short-period binary white dwarfs to exist for theoretical reasons. All calculations of the evolution of binary stars show that main-sequence binaries can evolve to binary white dwarfs (e.g., Iben and Tutukov 1984). Among Population I stars, 1/2 to 2/3 of all main-sequence stars are binaries and about 20% of these binaries should become double white dwarfs with short orbital periods (Abt 1983, Iben and Tutukov 1986). Thus, about 1/10 of all white dwarfs could be close binaries (Paczynski 1985). Nevertheless, no detached binary white dwarfs with extremely short periods have yet been found.

scholarly journals The role of the radiation pressure gradient in giant and supergiant star evolution

1984 ◽  
Vol 105 ◽  
pp. 89-91
Author(s):  
Wendee M. Brunish ◽  
Arthur N. Cox ◽  
Stephen A. Becker ◽  
Keith H. Despain
Keyword(s):  
Pressure Gradient ◽  
Radiation Pressure ◽  
Main Sequence ◽  
Red Giants ◽  
Physical Processes ◽  
Main Sequence Stars ◽  
Star Evolution ◽  
Supergiant Star

Since some of the earliest evolutionary calculations it has been found that post main sequence stars become red giants (e.g. Sandage and Schwarzschild, 1952). However the exact physical processes that lead to and determine the rate of redward evolution are not completely understood.

scholarly journals VINCI/VLTI Observations of Main Sequence Stars

2004 ◽  
Vol 219 ◽  
pp. 80-84
Author(s):  
Pierre Kervella ◽  
Frédéric Thévenin ◽  
Pierre Morel ◽  
Janine Provost ◽  
Gabrielle Berthomieu ◽  
...  
Keyword(s):  
Main Sequence ◽  
Extrasolar Planets ◽  
Physical Processes ◽  
Main Sequence Stars ◽  
M Dwarfs ◽  
The Past ◽  
Wide Range ◽  
Solar Type ◽  
The Universe ◽  
Angular Diameters

Main Sequence (MS) stars are by far the most numerous class in the Universe. They are often somewhat neglected as they are relatively quiet objects (but exceptions exist), though they bear testimony of the past and future of our Sun. An important characteristic of the MS stars, particularly the solar-type ones, is that they host the large majority of the known extrasolar planets. Moreover, at the bottom of the MS, the red M dwarfs pave the way to understanding the physics of brown dwarfs and giant planets. We have measured very precise angular diameters from recent VINCI/VLTI interferometric observations of a number of MS stars in the K band, with spectral types between A1V and M5.5V. They already cover a wide range of effective temperatures and radii. Combined with precise Hipparcos parallaxes, photometry, spectroscopy as well as the asteroseismic information available for some of these stars, the angular diameters put strong constraints on the detailed models of these stars, and therefore on the physical processes at play.

scholarly journals Origins of Hot Jupiters

2018 ◽  
Vol 56 (1) ◽  
pp. 175-221 ◽  
Author(s):  
Rebekah I. Dawson ◽  
John Asher Johnson
Keyword(s):  
Solar System ◽  
Main Sequence ◽  
Planetary Systems ◽  
Main Sequence Stars ◽  
High Eccentricity ◽  
Hot Jupiters ◽  
In Situ Formation ◽  
Tidal Migration ◽  
Hot Jupiter

Hot Jupiters were the first exoplanets to be discovered around main sequence stars and astonished us with their close-in orbits. They are a prime example of how exoplanets have challenged our textbook, solar-system inspired story of how planetary systems form and evolve. More than twenty years after the discovery of the first hot Jupiter, there is no consensus on their predominant origin channel. Three classes of hot Jupiter creation hypotheses have been proposed: in situ formation, disk migration, and high-eccentricity tidal migration. Although no origin channel alone satisfactorily explains all the evidence, two major origin channels together plausibly account for properties of hot Jupiters themselves and their connections to other exoplanet populations.

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