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Register a new userObservational evidence for two distinct giant planet populations
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Analysis of the statistical properties of exoplanets, together with those of their host stars, are providing a unique view into the process of planet formation and evolution. In this paper we explore the properties of the mass distribution of giant planet companions to solar-type stars, in a quest for clues about their formation process. With this goal in mind we studied, with the help of standard statistical tests, the mass distribution of giant planets using data from the exoplanet.eu catalog and the SWEET-Cat database of stellar parameters for stars with planets. We show that the mass distribution of giant planet companions is likely to present more than one population with a change in regime around 4,M$_{Jup}$. Above this value host stars tend to be more metal poor and more massive and have [Fe/H] distributions that are statistically similar to those observed in field stars of similar mass. On the other hand, stars that host planets below this limit show the well-known metallicity-giant planet frequency correlation. We discuss these results in light of various planet formation models and explore the implications they may have on our understanding of the formation of giant planets. In particular, we discuss the possibility that the existence of two separate populations of giant planets indicates that two different processes of formation are at play.
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Type Ia supernovae (SNe Ia) have been used as excellent standardizable candles for measuring cosmic expansion, but their progenitors are still elusive. Here we report that the spectral diversity of SNe Ia is tied to their birthplace environments. We find that those with high-velocity ejecta are substantially more concentrated in the inner and brighter regions of their host galaxies than are normal-velocity SNe Ia. Furthermore, the former tend to inhabit larger and more-luminous hosts. These results suggest that high-velocity SNe Ia likely originate from relatively younger and more metal-rich progenitors than normal-velocity SNe Ia, and are restricted to galaxies with substantial chemical evolution.
The current giant planet region is a transitional zone where transneptunian objects (TNOs) cross in their way to becoming Jupiter Family Comets (JFCs). Their dynamical behavior is conditioned by the intrinsic dynamical features of TNOs and also by the encounters with the giant planets. We address the Giant Planet Crossing (GPC) population (those objects with $5.2$ au $ < q < 30$ au) studying their number and their evolution from their sources, considering the current configuration of the Solar System. This subject is reviewed from previous investigations and also addressed by new numerical simulations of the dynamical evolution of Scattered Disk Objects (SDOs). We obtain a model of the intrinsic orbital element distribution of GPCs. The Scattered Disk represents the main source of prograde GPCs and Centaurs, while the contribution from Plutinos lies between one and two orders of magnitude below that from the SD. We obtain the number and size distribution of GPCs from our model, computing 9600 GPCs from the SD with $D > 100$ km and $sim 10^8$ with $D > 1$ km in the current population. The contribution from other sources is considered negligible. The mean lifetime in the Centaur zone is 7.2 Myr, while the mean lifetime of SDOs in the GPC zone is of 68 Myr. The latter is dependent on the initial inclination, being the ones with high inclinations the ones that survive the longest in the GPC zone. There is also a correlation of lifetime with perihelion distance, where greater perihelion leads to longer lifetime. The dynamical evolution of observed GPCs is different for prograde and retrograde objects. Retrograde GPCs have lower median lifetime than prograde ones, thus experiencing a comparatively faster evolution. However, it is probable that this faster evolution is due to the fact that the majority of retrograde GPCs have low perihelion values and then, lower lifetimes.
In Papers I and II of this series, the existence of two distinct halo populations of stars have been found in the solar neighborhood. Precise relative ages and orbital parameters are determined for 67 halo and 16 thick-disk stars having metallicities in the range -1.4 < [Fe/H] < -0.4 to better understand the context of the two halo populations in the formation and evolution of the Galaxy. Ages are derived by comparing the positions of stars in the logT_{eff}-log(g) diagram with isochrones from the Y^2 models interpolated to the exact [Fe/H] and [alpha/Fe] values of each star. Possible systematic errors in T_{eff} and log(g) are considered and corrected. With space velocities from Paper I as initial conditions, orbital integrations have been carried out using a detailed, observationally constrained Milky Way model including a bar and spiral arms. The `high-alpha halo stars have ages 2-3 Gyr larger than the `low-alpha ones. The orbital parameters show very distinct differences between the `high-alpha and `low-alpha halo stars. The `low-alpha ones have r_{max}s to 30-40 kpc, z_{max}s to approx. 18 kpc, and e_{max}s clumped at values greater than 0.85, while the `high-alpha ones, r_{max}s to about 16 kpc, z_{max}s to 6-8 kpc, and e_{max} more or less uniformly distributed over 0.4-1.0. A dual in situ-plus-accretion formation scenario best explains the existence and characteristics of these two halo populations, but one remaining defect is that this model is not consistent regarding the r_{max}s obtained for the in situ `high-alpha component; the predicted values are too small. It appears that omega Cen may have contributed in a significant way to the existence of the `low-alpha component; recent models, including dynamical friction and tidal stripping, have produced orbital parameters as great as those of the `low-alpha component.
We present the discovery of the transiting exoplanets HAT-P-65b and HAT-P-66b, with orbital periods of 2.6055 d and 2.9721 d, masses of $0.527 pm 0.083$ M$_{J}$ and $0.783 pm 0.057$ M$_{J}$ and inflated radii of $1.89 pm 0.13$ R$_{J}$ and $1.59^{+0.16}_{-0.10}$ R$_{J}$, respectively. They orbit moderately bright ($V=13.145 pm 0.029$, and $V=12.993 pm 0.052$) stars of mass $1.212 pm 0.050$ M$_{odot}$ and $1.255^{+0.107}_{-0.054}$ M$_{odot}$. The stars are at the main sequence turnoff. While it is well known that the radii of close-in giant planets are correlated with their equilibrium temperatures, whether or not the radii of planets increase in time as their hosts evolve and become more luminous is an open question. Looking at the broader sample of well-characterized close-in transiting giant planets, we find that there is a statistically significant correlation between planetary radii and the fractional ages of their host stars, with a false alarm probability of only 0.0041%. We find that the correlation between the radii of planets and the fractional ages of their hosts is fully explained by the known correlation between planetary radii and their present day equilibrium temperatures, however if the zero-age main sequence equilibrium temperature is used in place of the present day equilibrium temperature then a correlation with age must also be included to explain the planetary radii. This suggests that, after contracting during the pre-main-sequence, close-in giant planets are re-inflated over time due to the increasing level of irradiation received from their host stars. Prior theoretical work indicates that such a dynamic response to irradiation requires a significant fraction of the incident energy to be deposited deep within the planetary interiors.
We present a study of the relationship between black hole accretion rate (BHAR) and star formation rate (SFR) in a sample of giant elliptical galaxies. These galaxies, which live at the centers of galaxy groups and clusters, have star formation and black hole activity that is primarily fueled by gas condensing out of the hot intracluster medium. For a sample of 46 galaxies spanning 5 orders of magnitude in BHAR and SFR, we find a mean ratio of log(BHAR/SFR) = -1.45 +/- 0.2, independent of the methodology used to constrain both SFR and BHAR. This ratio is significantly higher than most previously-published values for field galaxies. We investigate whether these high BHAR/SFR ratios are driven by high BHAR, low SFR, or a different accretion efficiency in radio galaxies. The data suggest that the high BHAR/SFR ratios are primarily driven by boosted black hole accretion in spheroidal galaxies compared to their disk counterparts. We propose that angular momentum of the cool gas is the primary driver in suppressing BHAR in lower mass galaxies, with massive galaxies accreting gas that has condensed out of the hot phase on nearly radial trajectories. Additionally, we demonstrate that the relationship between specific BHAR and SFR has much less scatter over 6 orders of magnitude in both parameters, due to competing dependence on morphology between the M_BH--M_* and BHAR--SFR relations. In general, active galaxies selected by typical techniques have sBHAR/sSFR ~ 10, while galactic nuclei with no clear AGN signatures have sBHAR/sSFR ~ 1, consistent with a universal M_BH--M_spheroid relation.
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