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Register a new userA hot Jupiter for breakfast? --- Early stellar ingestion of planets may be common
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Models of planet formation and evolution predict that giant planets form efficiently in protoplanetary disks, that most of these migrate rapidly to the disks inner edge, and that, if the arriving planets mass is $lesssim$ Jupiters mass, it could remain stranded near that radius. We argue that such planets would be ingested by tidal interaction with the host star on a timescale $lesssim1,$Gyr, and that, in the case of a solar-type host, this would cause the stellar spin to approach the direction of the ingested planets orbital axis even if the two were initially highly misaligned. Primordially misaligned stars whose effective temperatures are $gtrsim6250,$K cannot be realigned in this way because, in contrast with solar-type hosts, their angular momenta are typically higher than the orbital angular momentum of the ingested planet as a result of inefficient magnetic braking and of a comparatively large moment of inertia. Hot Jupiters located farther out from the star can contribute to this process, but their effect is weaker because the tidal interaction strength decreases rapidly with increasing semimajor axis. We demonstrate that, if $sim50%$ of planetary systems harbored a stranded hot Jupiter, this scenario can in principle account for (1) the good alignment exhibited by planets around cool stars irrespective of the planets mass or orbital period, (2) the prevalence of misaligned planets around hot stars, (3) the apparent upper bound on the mass of hot Jupiters on retrograde orbits, and (4) the inverse correlation between stellar spin periods and hot-Jupiter masses.
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When the Sun ascends the red giant branch (RGB), its luminosity will increase and all the planets will receive much greater irradiation than they do now. Jupiter, in particular, might end up more highly irradiated than the hot Neptune GJ 436b and, hence, could appropriately be termed a hot Jupiter. When their stars go through the RGB or asymptotic giant branch (AGB) stages, many of the currently known Jupiter-mass planets in several-AU orbits will receive levels of irradiation comparable to the hot Jupiters, which will transiently increase their atmospheric temperatures to ~1000 K or more. Furthermore, massive planets around post-main-sequence stars could accrete a non-negligible amount of material from the enhanced stellar winds, thereby significantly altering their atmospheric chemistry as well as causing a significant accretion luminosity during the epochs of most intense stellar mass loss. Future generations of infrared observatories might be able to probe the thermal and chemical structure of such hot Jupiters atmospheres. Finally, we argue that, unlike their main-sequence analogs (whose zonal winds are thought to be organized in only a few broad, planetary-scale jets), red-giant hot Jupiters should have multiple, narrow jets of zonal winds and efficient day-night redistribution.
We hypothesize that hot Jupiters with inflated sizes represent a separate planet formation channel,the merging of two low-mass stars. We show that the abundance and properties of W UMa stars and low mass detached binaries are consistent with their being possible progenitors. The degree of inflation of the transiting hot Jupiters correlates with their expected spiral-in life time by tidal dissipation, and this could indicate youth if the stellar dissipation parameter Q* is sufficiently low. Several Jupiter-mass planets can form in the massive compact disk formed in a merger event. Gravitational scattering between them can explain the high incidence of excentric, inclined, and retrograde orbits. If the population of inflated planets is indeed formed by a merger process, their frequency should be much higher around blue stragglers than around T Tauri stars.
We present evidence for a correlation between the observed properties of hot Jupiter emission spectra and the activity levels of the host stars measured using Ca II H & K emission lines. We find that planets with dayside emission spectra that are well-described by standard 1D atmosphere models with water in absorption (HD 189733, TrES-1, TrES-3, WASP-4) orbit chromospherically active stars, while planets with emission spectra that are consistent with the presence of a strong high-altitude temperature inversion and water in emission orbit quieter stars. We estimate that active G and K stars have Lyman alpha fluxes that are typically a factor of 4-7 times higher than quiet stars with analogous spectral types, and propose that the increased UV flux received by planets orbiting active stars destroys the compounds responsible for the formation of the observed temperature
Using the prospector spectral energy distribution (SED) fitting code, we analyze the properties of 19 Extreme Emission Line Galaxies (EELGs) identified in the bluest composite SED in the zfourge survey at $2.5 leq z leq 4$. prospector includes a physical model for nebular emission and returns probability distributions for stellar mass, stellar metallicity, dust attenuation, and nonparametric star formation history (SFH). The EELGs show evidence for a starburst in the most recent 50 Myr, with the median EELG having a specific star formation rate (sSFR) of 4.6 Gyr$^{-1}$ and forming 15% of its mass in this short time. For a sample of more typical star-forming galaxies (SFGs) at the same redshifts, the median SFG has a sSFR of 1.1 Gyr$^{-1}$ and forms only $4%$ of its mass in the last 50 Myr. We find that virtually all of our EELGs have rising SFHs, while most of our SFGs do not. From our analysis, we hypothesize that many, if not most, star-forming galaxies at $z geq 2.5$ undergo an extreme H$beta$+$[hbox{{rm O}kern 0.1em{sc iii}}]$ emission line phase early in their lifetimes. In a companion paper, we obtain spectroscopic confirmation of the EELGs as part of our {sc MOSEL} survey. In the future, explorations of uncertainties in modeling the UV slope for galaxies at $z>2$ are needed to better constrain their properties, e.g. stellar metallicities.
We report on the confirmation of a transiting giant planet around the relatively hot (Teff = 6801 $pm$ 56 K) star HD2685, whose transit signal was detected in Sector 1 data of the TESS mission. We confirmed the planetary nature of the transit signal by using Doppler velocimetric measurements with CHIRON, CORALIE and FEROS, as well as photometric data with CHAT and LCOGT. From the photometry and radial velocities joint analysis, we derived the following parameters for HD2685 $b$: $P$=4.12692$pm$0.00004 days, M$_P$=1.18 $pm$ 0.09 $M_J$ and $R_P$=1.44 $pm$ 0.01 $R_J$. This system is a typical example of an inflated transiting Hot-Jupiter in a circular orbit. Given the host star apparent visual magnitude ($V$ = 9.6 mag), this is one of the brightest known stars hosting a transiting Hot-Jupiter, and a good example of the upcoming systems that will be detected by TESS during the two-year primary mission. This is also an excellent target for future ground and space based atmospheric characterization as well as a good candidate for measuring the projected spin-orbit misalignment angle via the Rossiter-McLaughlin effect.
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