The occurrence and the distribution of masses and radii of exoplanets

AbstractWe analyze the statistics of Doppler-detected planets and Keplere-detected planet candidates of high integrity. We determine the number of planets per star as a function of planet mass, radius, and orbital period, and the occurrence of planets as a function of stellar mass. We consider only orbital periods less than 50 days around Solar-type (GK) stars, for which both Doppler and Kepler offer good completeness. We account for observational detection effects to determine the actual number of planets per star. From Doppler-detected planets discovered in a survey of 166 nearby G and K main sequence stars we find a planet occurrence of 15+5−4% for planets with M sin i = 3–30 ME and P < 50 d, as described in Howard et al. (2010). From Keplere, the planet occurrence is 0.130 ± 0.008, 0.023 ± 0.003, and 0.013 ± 0.002 planets per star for planets with radii 2–4, 4–8, and 8–32 RE, consistent with Doppler-detected planets. From Keplere, the number of planets per star as a function of planet radius is given by a power law, df/dlog R = kRRα with kR = 2.9+0.5−0.4, α = −1.92 ± 0.11, and R = RP/RE. Neither the Doppler-detected planets nor the Keplere-detected planets exhibit a “desert” at super-Earth and Neptune sizes for close-in orbits, as suggested by some planet population synthesis models. The distribution of planets with orbital period, P, shows a gentle increase in occurrence with orbital period in the range 2–50 d. The occurrence of small, 2–4 RE planets increases with decreasing stellar mass, with seven times more planets around low mass dwarfs (3600–4100 K) than around massive stars (6600–7100 K).

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The Evolutionary Status of the Secondaries of Cataclysmic Binaries

International Astronomical Union Colloquium ◽

10.1017/s0252921100090394 ◽

1983 ◽

Vol 72 ◽

pp. 257-262

Author(s):

H. Ritter

Keyword(s):

Probability Distribution ◽

Main Sequence ◽

The Other ◽

Initial Mass ◽

Evolutionary Status ◽

Mass Ratio ◽

Main Sequence Stars ◽

Cataclysmic Binaries ◽

Low Mass ◽

Orbital Periods

ABSTRACTIt is shown that the secondary components of cataclysmic binaries with orbital periods of less than ~10 hours are indistinguishable from ordinary low-mass main-sequence stars and that, therefore, they are essentially unevolved. On the other hand, it is shown that, depending on the mass ratio of the progenitor system, the secondary of a cataclysmic binary could be significantly evolved. The fact that nevertheless most of the observed secondaries are essentially unevolved can be accounted for by assuming that the probability distribution for the initial mass ratio is not strongly peaked towards unity mass ratio.

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Testing planet formation theories with giant stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308016621 ◽

2007 ◽

Vol 3 (S249) ◽

pp. 209-222

Author(s):

Luca Pasquini ◽

M.P. Döllinger ◽

A. Hatzes ◽

J. Setiawan ◽

L. Girardi ◽

...

Keyword(s):

Main Sequence ◽

Planet Formation ◽

Mass Range ◽

Stellar Mass ◽

Giant Planets ◽

Main Sequence Stars ◽

Giant Stars ◽

Solar Type ◽

The Subject ◽

Host Stars

AbstractPlanet searches around evolved giant stars are bringing new insights to planet formation theories by virtue of the broader stellar mass range of the host stars compared to the solar-type stars that have been the subject of most current planet searches programs. These searches among giant stars are producing extremely interesting results. Contrary to main sequence stars planet-hosting giants do not show a tendency of being more metal rich. Even if limited, the statistics also suggest a higher frequency of giant planets (at least 10%) that are more massive compared to solar-type main sequence stars.The interpretation of these results is not straightforward. We propose that the lack of a metallicity-planet connection among giant stars is due to pollution of the star while on the main sequence, followed by dillution during the giant phase. We also suggest that the higher mass and frequency of the planets are due to the higher stellar mass. Even if these results do not favor a specific formation scenario, they suggest that planetary formation might be more complex than what has been proposed so far, perhaps with two mechanisms at work and one or the other dominating according to the stellar mass. We finally stress as the detailed study of the host stars and of the parent sample is essential to derive firm conclusions.

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Black widow formation by pulsar irradiation and sustained magnetic braking

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3358 ◽

2020 ◽

Vol 500 (2) ◽

pp. 1592-1603

Author(s):

Sivan Ginzburg ◽

Eliot Quataert

Keyword(s):

Main Sequence ◽

High Energy ◽

Roche Lobe ◽

Main Sequence Stars ◽

Black Widow ◽

High Energy Radiation ◽

Night Side ◽

Low Mass ◽

Magnetic Braking ◽

Orbital Periods

ABSTRACT Black widows are millisecond pulsars with low-mass companions, a few per cent the mass of the sun, on orbits of several hours. These companions are presumably the remnants of main-sequence stars that lost their mass through a combination of Roche lobe overflow and ablation by the host pulsar’s high-energy radiation. While ablation itself is too weak to significantly reduce the mass of the companion star, the ablated wind couples to its magnetic field, removes orbital angular momentum, and thus maintains stable Roche lobe overflow. We use the mesa stellar evolution code, complemented by analytical estimates, to track initially main-sequence companions as they are reduced to a fraction of their original mass by this ablation-driven magnetic braking. We argue that magnetic braking remains effective even for low-mass companions. A key ingredient of our model is that the irradiating luminosity of the pulsar Lirr deposits energy in the companion’s atmosphere and thereby slows down its Kelvin–Helmholtz cooling. We find that the high-energy luminosities measured by Fermi $L_{\rm irr}=0.1\rm {-}3$ L⊙ can explain the span of black widow orbital periods. The same Lirr range reproduces the companions’ night-side temperatures, which cluster around 3000 K, as inferred from optical light curves.

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Doppler Detection of Extrasolar Planets

International Astronomical Union Colloquium ◽

10.1017/s0252921100048466 ◽

1999 ◽

Vol 170 ◽

pp. 121-130

Author(s):

G. W. Marcy ◽

R. Paul Butler ◽

D. A. Fischer

Keyword(s):

Main Sequence ◽

Extrasolar Planets ◽

Mass Function ◽

Solar Neighborhood ◽

Main Sequence Stars ◽

Low Mass Stars ◽

Pile Up ◽

Solar Type ◽

Low Mass ◽

M Dwarf

AbstractWe have measured the radial velocities of 540 G and K main sequence stars with a precision of 3−10 ms−1 using the Lick and Keck échelle spectrometers. We had detected 6 companions that have m sin i < 7 MJup. We announce here the discovery of a new planet around Gliese 876, found in our Doppler measurements from both Lick and Keck. This is the first planet found around an M dwarf, which indicates that planets occur around low-mass stars, in addition to solar-type stars. We combine our entire stellar sample with that of Mayor et al. to derive general properties of giant planets within a few AU of these stars. Less than 1% of G and K main sequence stars harbor brown dwarf companions with masses between 5 and 70 MJup. Including Gliese 876b, 8 companions exhibit m sin i < 5 MJup which constitute the best planet candidates to date. Apparently, 4% of stars have planetary companions within the range m sin i = 0.5 to 5 MJup. Planets are distinguished from brown dwarfs by the discontinuous jump in the mass function at 5 MJup. About 2/3 of the planets orbit within just 0.3 AU due in part to their favorable detectability, but also possibly due to a real “pile up” of planets near the star. Inward orbital migration after formation may explain this, but the mechanism to stop the migration remains unclear. Five of eight planets have orbital eccentricities greater than that of our Jupiter, eJup = 0.048, and tidal circularization may explain most of the circular orbits. Thus, eccentric orbits are common and may arise from gravitational interactions with other planets, stars, or the protoplanetary disk. The planet-bearing stars are systematically metal-rich, as is the Sun, compared to the solar neighborhood.

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

International Astronomical Union Colloquium ◽

10.1017/s0252921100100132 ◽

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.

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Theoretical estimates of the convective turnover time for low-mass, rotating pre-main sequence stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307000889 ◽

2006 ◽

Vol 2 (S239) ◽

pp. 446-448

Author(s):

L. T. S. Mendes ◽

N. R. Landin ◽

L. P. R. Vaz

Keyword(s):

Main Sequence ◽

Empirical Relationship ◽

Magnetic Activity ◽

Turnover Time ◽

Main Sequence Stars ◽

Full Spectrum ◽

Solar Type ◽

Low Mass ◽

Mixing Length Theory ◽

Semi Empirical

AbstractThe Rossby number Ro is an important quantity related to the well-known magnetic activity-rotation correlation for main sequence, solar-type stars. For such stars, Ro can be obtained by a semi-empirical relationship between the convective turnover time τc and the B-V colour index, but an equivalent activity-rotation correlation seems not to exist for pre-main sequence stars. In this work we report theoretical estimates of τc for low-mass, rotating pre-main sequence stars under either the Full Spectrum of Turbulence (FST) or the classical Mixing Length Theory (MLT) convection models. The results for the MLT models show that the lower the convection efficiency the higher τc, while the FST models give τc lower than those for the MLT. The presence of a parametric magnetic field lowers the convection efficiency, resulting in smaller τc values.

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The Mass Distribution of Secondaries to Solar-Type Stars

International Astronomical Union Colloquium ◽

10.1017/s025292110000840x ◽

2004 ◽

Vol 191 ◽

pp. 37-40 ◽

Cited By ~ 1

Author(s):

Helmut A. Abt ◽

Daryl W. Willmarth

Keyword(s):

Radial Velocity ◽

Mass Distribution ◽

Main Sequence ◽

Mass Function ◽

Spectroscopic Binaries ◽

Orbital Elements ◽

Main Sequence Stars ◽

Solar Type ◽

Low Mass ◽

Good Agreement

AbstractTwo previous studies of the secondary mass function in spectroscopic binaries by Abt & Levy (1976) and by Duquennoy & Mayor (1991) are shown to be in good agreement if they are both plotted with the same abscissa scale. A new study of 271 main-sequence stars later than F6 V made with a radial-velocity accuracy of ±0.10 km s-1 yielded 10 new sets of orbital elements in addition to the 59 published ones. The resulting secondary mass function is nearly flat and shows that 2.2±1.5% of the primaries have low-mass (0.01–0.10 M⊙) companions. In contrast, the secondary mass function for visual binaries with separations >500 AU fits a van Rhijn function, as was shown previously by Abt and Levy.

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Are sdAs helium core stars?

Open Astronomy ◽

10.1515/astro-2017-0433 ◽

2017 ◽

Vol 26 (1) ◽

Cited By ~ 4

Author(s):

Ingrid Pelisoli ◽

S. O. Kepler ◽

Detlev Koester

Keyword(s):

Main Sequence ◽

Galactic Disk ◽

Physical Nature ◽

Sloan Digital Sky Survey ◽

Distance Modulus ◽

Main Sequence Stars ◽

Sky Survey ◽

Balmer Lines ◽

Low Mass ◽

Binary Evolution

AbstractEvolved stars with a helium core can be formed by non-conservative mass exchange interaction with a companion or by strong mass loss. Their masses are smaller than 0.5 M⊙. In the database of the Sloan Digital Sky Survey (SDSS), there are several thousand stars which were classified by the pipeline as dwarf O, B and A stars. Considering the lifetimes of these classes on the main sequence, and their distance modulus at the SDSS bright saturation, if these were common main sequence stars, there would be a considerable population of young stars very far from the galactic disk. Their spectra are dominated by Balmer lines which suggest effective temperatures around 8 000-10 000 K. Several thousand have significant proper motions, indicative of distances smaller than 1 kpc. Many show surface gravity in intermediate values between main sequence and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars. Their physical nature and evolutionary history remains a puzzle. We propose they are not H-core main sequence stars, but helium core stars and the outcomes of binary evolution. We report the discovery of two new extremely-low mass white dwarfs among the sdAs to support this statement.

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