Terrestrial planets across space and time

The study of cosmology, galaxy formation and exoplanets has now advanced to a stage where a cosmic inventory of terrestrial planets may be attempted. By coupling semi-analytic models of galaxy formation to a recipe that relates the occurrence of planets to the mass and metallicity of their host stars, we trace the population of terrestrial planets around both solar-mass (FGK type) and lower-mass (M dwarf) stars throughout all of cosmic history. We find that the mean age of terrestrial planets in the local Universe is $7\pm{}1$ Gyr for FGK hosts and $8\pm{}1$ Gyr for M dwarfs. We estimate that hot Jupiters have depleted the population of terrestrial planets around FGK stars by no more than $\approx 10\%$, and that only $\approx 10\%$ of the terrestrial planets at the current epoch are orbiting stars in a metallicity range for which such planets have yet to be confirmed. The typical terrestrial planet in the local Universe is located in a spheroid-dominated galaxy with a total stellar mass comparable to that of the Milky Way. When looking at the inventory of planets throughout the whole observable Universe, we argue for a total of $\approx 1\times 10^{19}$ and $\approx 5\times 10^{20}$ terrestrial planets around FGK and M stars, respectively. Due to light travel time effects, the terrestrial planets on our past light cone exhibit a mean age of just $1.7\pm 0.2$ Gyr. These results are discussed in the context of cosmic habitability, the Copernican principle and searches for extraterrestrial intelligence at cosmological distances.Comment: 11 pages, 8 figures. v.2: Accepted for publication in ApJ. Some changes in quantitative results compared to v.1, mainly due to differences in IMF assumption

Benchmarking Gaia DR3 Apsis with the Hyades and Pleiades open clusters

The Gaia astrophysical parameters inference system (Apsis) provides astrophysical parameter estimates for several to 100s of millions of stars. We aim to benchmark Gaia DR3 Apsis. We have compiled about 1500 bona fide single stars in the Hyades and Pleiades open clusters for validation of PARSEC isochrones, and for comparison with Apsis estimates. PARSEC stellar isochrones in the Gaia photometric system enable us to assign average ages and metallicities to the clusters, and mass, effective temperature, luminosity, and surface gravity to the individual stars. Apsis does not recover the single-age, single-metallicity characteristic of the cluster populations. Ages assigned to cluster members seemingly follow the input template for Galactic populations, with earlier-type stars systematically being assigned younger ages than later-type stars. Cluster metallicities are underestimated by 0.1 to 0.2 dex. Effective temperature estimates are in general reliable. Surface gravity estimates reveal strong systematics for specific ranges of Gaia BP-RP colours. We caution that Gaia DR3 Apsis estimates can be subject to significant systematics. Some of the Apsis estimates, like metallicity, might only be meaningful for statistical studies of the time-averaged Galactic stellar population, but are not recommended to be used for individual stars.Comment: Accepted for publication in A&A. Table 2 in its entirety can be requested from the authors in machine-readable format (mrt), and will become available via CDS. 8 pages, 6 figures. v2: Figure 6, right, updated based on Gaia DR3 Apsis GSP-Spec quality flag

Characterising Young Visual M-dwarf Binaries with Near-Infrared Integral Field Spectra

We present the results from an integral field spectroscopy study of seven close visual binary pairs of young M-dwarf multiple systems. The target systems are part of the astrometric monitoring AstraLux program, surveying hundreds of M-dwarf systems for multiplicity and obtaining astrometric epochs for orbital constraints. Our new VLT/SINFONI data provides resolved spectral type classification in the J, H and K bands for seven of these low-mass M-dwarf binaries, which we determine by comparing them to empirical templates and examining the strength of water absorption in the K-band. The medium resolution K-band spectra also allows us to derive effective temperatures for the individual components. All targets in the survey display several signs of youth, and some have kinematics similar to young moving groups, or low surface gravities which we determine from measuring equivalent widths of gravity sensitive alkali lines in the J-band. Resolved photometry from our targets is also compared with isochrones from theoretical evolutionary models, further implying young ages. Dynamical masses will be provided from ongoing monitoring of these systems, which can be seen as emblematic binary benchmarks that may be used to calibrate evolutionary models for low-mass stars in the future.Comment: 12 pages, 5 figures, 8 tables, preprint, accepted for publication in A&

The discrepancy between dynamical and theoretical mass in the triplet-system 2MASS J10364483+1521394

We combine new Lucky Imaging astrometry from NTT/AstraLux Sur with already published astrometry from the AstraLux Large M-dwarf Multiplicity Survey to compute orbital elements and individual masses of the 2MASS J10364483+1521394 triple system belonging to the Ursa-Major moving group. The system consists of one primary low-mass M-dwarf orbited by two less massive companions, for which we determine a combined dynamical mass of $M_{\rm{B}+\rm{C}}= 0.48 \pm 0.14\ M_\odot$. We show from the companions relative motions that they are of equal mass (with a mass ratio of$1.00 \pm 0.03$), thus$0.24 \pm 0.07\ M_\odot$individually, with a separation of$3.2 \pm 0.3\ $AU and conclude that these masses are significantly higher ($30\%$) than what is predicted by theoretical stellar evolutionary models. The biggest uncertainty remains the distance to the system, here adopted as$20.1 \pm 2.0$pc based on trigonometric parallax, whose ambiguity has a major impact on the result. With the new observational data we are able to conclude that the orbital period of the BC pair is$8.41^{+0.04}_{-0.02}\ $years.Comment: 9 pages, 7 figures, accepted for publication in Astronomy & Astrophysic

Spectral characterization of newly detected young substellar binaries with SINFONI

We observe 14 young low-mass substellar objects in young moving groups using the SINFONI IFS with LGS-AO to detect and characterize 3 candidate binary systems. Together with the adopted young moving group ages we employ isochrones from substellar evolutionary models to estimate individual masses for the binaries. We find 2MASS J15104786-2818174 to be part of the $\approx 30 - 50$ Myr Argus moving group and composed of a $34 - 48\,M_{\rm Jup}$ primary brown dwarf with spectral type M$9\gamma$ and a fainter $15 - 22\, M_{\rm Jup}$ companion, separated by $\approx 100$ mas. 2MASS J22025794-5605087 is identified as an almost equal-mass binary in the AB Dor moving group, with a projected separation of $\approx 60$ mas. Both components share spectral type M$9\gamma/\beta$, which with the adopted age of $120 - 200$ Myr yields individual masses between $50 - 68\,M_{\rm Jup}$. The observations of 2MASS J15474719-2423493 are of lesser quality and we obtain no spectral characterization for the target, but resolve two components separated by $\approx 170$ mas which with the predicted young field age of $30 - 50$ Myr yields individual masses below $20\,M_{\rm Jup}$. Out of the 3 candidate binary systems, 2MASS J22025794-5605087 has unambiguous spectroscopic signs of being a bona-fide binary, while the other two will require second-epoch confirmation. The small projected separations between the binary components corresponds to physical separations of $\approx 4 - 7$ AU, allowing for astrometric monitoring of just a few years in order to generate constrained orbital fits and dynamical masses for the systems. In combination with their young ages, these binaries will prove to be excellent benchmarks for calibrating substellar evolutionary models down to a very low-mass regime.Comment: 17 pages, 14 figure

Benchmarking mesa isochrones against the Hyades single star sequence

Based on GAIA Early Data Release 3 (EDR3), we revisit and update our sample of bonafide single stars in the Hyades open cluster. The small observational uncertainties in parallax and photometry of EDR3 result in a tightly defined stellar sequence, which is ideal for the testing and calibration of theoretical stellar evolutionary tracks and isochrones. We benchmark the solar-scaled mesa evolutionary models against the single star sequence. We find that the non-rotating mesa models for [Fe/H] = +0.25 provide a good fit for stars with masses above 0.85, and very low mass stars below 0.25 M⊙. For stars with masses between 0.25 and 0.85 M⊙, the models systematically under predict the observed stellar luminosity. One potential limitation of the models for partially convective stars more massive than 0.35 M⊙ is the prescription of (superadiabatic) convection with the mixing-length theory parameter αML tuned to match the Solar model. Below 0.35 M⊙, the increased scatter in the stellar sequence might be a manifestation of the convective kissing instability, which is driven by variations in the 3He nuclear energy production rate due to instabilities at the convective core to envelope boundary. For a Hyades-like stellar population, the application of solar-scaled models to subsolar mass stars could result in a significant underestimate of the age, or an overestimate of the metallicity. We suggest that future grids of solar-scaled evolutionary stellar models could be complemented by Hyades-scaled models in the mass range 0.25 to 0.85 M⊙. © 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society

Probe for Measuring Soil Specific Heat Using A Heat-Pulse Method

Temperature rise, measured a short distance from a line heat source, can be used to determine the volumetric specific heat of soil and other materials. Volumetric specific heat is linearly related to the inverse of the temperature rise. The purpose of this note is to describe the construction and performance of a device for measuring specific heat using the line source method. The device was constructed from two hypodermic needles, 0.813 mm in diam. and 28 mm long, and spaced 6 mm apart. One needle contained a heater and the other a thermocouple. The temperature rise from heat pulses given to the heater were measured with the thermocouple. The coefficientof variation (CV) of specific heat on replicate samples was around 1%. Since water is the main variable component of the specific heat in nonswelling soil, changes in water content might be resolved to 0.01 or better in nonswelling soil

SPOTS: The Search for Planets Orbiting Two Stars. III. Complete Sample and Statistical Analysis

Binary stars constitute a large percentage of the stellar population, yet relatively little is known about the planetary systems orbiting them. Most constraints on circumbinary planets (CBPs) so far come from transit observations with the Kepler telescope, which is sensitive to close-in exoplanets but does not constrain planets on wider orbits. However, with continuous developments in high-contrast imaging techniques, this population can now be addressed through direct imaging. We present the full survey results of the Search for Planets Orbiting Two Stars (SPOTS) survey, which is the first direct imaging survey targeting CBPs. The SPOTS observational program comprises 62 tight binaries that are young and nearby, and thus suitable for direct imaging studies, with VLT/NaCo and VLT/SPHERE. Results from SPOTS include the resolved circumbinary disk around AK Sco, the discovery of a low-mass stellar companion in a triple packed system, the relative astrometry of up to 9 resolved binaries, and possible indications of non-background planetary-mass candidates around HIP 77911. We did not find any CBP within 300 AU, which implies a frequency upper limit on CBPs (1--15 $M_{\rm Jup}$) of 6--10 % between 30-300 AU. Coupling these observations with an archival dataset for a total of 163 stellar pairs, we find a best-fit CBP frequency of 1.9 % (2--15 $M_{\rm Jup}$) between 1--300 AU with a 10.5 % upper limit at a 95 % confidence level. This result is consistent with the distribution of companions around single stars.Comment: 27 pages, 13 Figures, 7 Tables. Accepted for publication in A&

JWST/NIRCam Coronagraphy of the Young Planet-hosting Debris Disk AU Microscopii

High-contrast imaging of debris disk systems permits us to assess the composition and size distribution of circumstellar dust, to probe recent dynamical histories, and to directly detect and characterize embedded exoplanets. Observations of these systems in the infrared beyond 2--3 $\mu$m promise access to both extremely favorable planet contrasts and numerous scattered-light spectral features -- but have typically been inhibited by the brightness of the sky at these wavelengths. We present coronagraphy of the AU Microscopii (AU Mic) system using JWST's Near Infrared Camera (NIRCam) in two filters spanning 3--5 $\mu$m. These data provide the first images of the system's famous debris disk at these wavelengths and permit additional constraints on its properties and morphology. Conducting a deep search for companions in these data, we do not identify any compelling candidates. However, with sensitivity sufficient to recover planets as small as $\sim 0.1$ Jupiter masses beyond $\sim 2^{\prime\prime}$ ($\sim 20$ au) with $5\sigma$ confidence, these data place significant constraints on any massive companions that might still remain at large separations and provide additional context for the compact, multi-planet system orbiting very close-in. The observations presented here highlight NIRCam's unique capabilities for probing similar disks in this largely unexplored wavelength range, and provide the deepest direct imaging constraints on wide-orbit giant planets in this very well studied benchmark system.Comment: 27 pages, 14 figure