Stars Of Spectral Types Research Articles

Planet-star interactions with precise transit timing

Context. Giant exoplanets on 1-3 day orbits, known as ultra-hot Jupiters, induce detectable tides in their host stars. The energy of those tides dissipates at a rate related to the properties of the stellar interior. At the same time, a planet loses its orbital angular momentum and spirals into the host star. The decrease in the orbital period is empirically accessible with precise transit timing and can be used to probe planet-star tidal interactions. Aims. Statistical studies show that stars of GK spectral types, with masses below 1.1 M⊙, are depleted in hot Jupiters. This finding is evidence of tidal orbital decay during the main-sequence lifetime. Theoretical considerations show that in some configurations the tidal energy dissipation can be boosted by non-linear effects in dynamical tides, which are wave-like responses to tidal forcing. To probe the regime of these dynamical tides in GK stars, we searched for orbital period shortening for six selected hot Jupiters in systems with 0.8–1 M⊙ host stars: HATS-18, HIP 65A, TrES-3, WASP-19, WASP-43, and WASP-173A. Methods. For the hot Jupiters in our sample, we analysed transit timing datasets based on mid-transit points homogeneously determined from observations performed with the Transiting Exoplanet Survey Satellite and high-quality data available in the literature. For the TrES-3 system, we also used new transit light curves we acquired with ground-based telescopes. We searched mid-transit times for shortening of orbital periods by statistically testing quadratic transit ephemerides. Theoretical predictions on the dissipation rate for dynamical tides were calculated under the regimes of internal gravity waves (IGWs) undergoing wave breaking (WB) in stellar centres and weak non-linear (WNL) wave-wave interactions in radiative layers. Stellar parameters of the host stars, such as mass and age, which were used in those computations, were homogeneously redetermined using evolutionary models with the Bayesian inference. Results. We found that transit times follow the refined linear ephemerides for all ultra-hot Jupiters of our sample. The non-detection of orbital decay allowed us to place lower constraints on the tidal dissipation rates in those planet-star systems. In three systems, HATS-18, WASP-19, and WASP-43, we reject a scenario with total dissipation of IGWs. We conclude that their giant planets are not massive enough to induce WB. Our observational constraints for HIP 65A, TrES-3, and WASP-173A are too weak to probe the WB regime. Calculations show that WB is not expected in the former two, leaving the WASP-173A system as a promising target for further transit timing observations. The WNL dissipation was tested in the WASP-19 and WASP-43 systems, showing that the theoretical dissipation rates are overestimated by at least one order of magnitude. For the remaining systems, decades or even centuries of transit timing measurements are needed to probe the WNL regime entirely. Among them, TrES-3 and WASP-173A have the predicted WNL dissipation rates that coincide with the values obtained from gyrochronology. Conclusions. Tidal dissipation in the GK stars of our sample is not boosted by WB in their radiative cores, preventing their giant planets from rapid orbital decay. Weakly non-linear tidal dissipation could drive orbital shrinkage and stellar spin-up on gigayear timescales. Although our first results suggest that theory might overestimate the dissipation rate and some fine-tuning would be needed for at least a fraction of planet-star configurations, some predictions coincide intriguingly with the gyrochronological estimates. We identify the WASP-173A system as a promising candidate for exploring this problem in the shortest possible time of the coming decades.

Differential Rotation of CoRoT Stars and a Kepler Binary Star from Starspot Transit Mapping

Abstract While direct magnetic field measurements are rare for slowly rotating stars, spots observed during planetary transits provide a potential indicator of magnetic activity on stellar surfaces. Moreover, the rotation of the stellar surface can be probed by monitoring the spots’ position with time in subsequent transits. This study investigates the dynamic interplay of rotational shear and stellar rotation rate in six stars of spectral types F to M, all hosting exoplanets observed by the CoRoT space mission, except for one binary star from Kepler. The analysis, facilitated by the ECLIPSE code, unveils the physical properties of stellar spots, including radius, intensity, temperature, and position. The five CoRoT stars exhibit spot characteristics consistent with those observed in solar type stars. The determination of a spot longitude during different transits allows for the inference of the star’s differential rotation profile, revealing a decreasing trend of rotational shear with the mean stellar rotation period, given by Δ Ω ∝ P ¯ − 0.9 . This implies that, at least for slow rotators (mean rotation period >5 days), as stars age, their differential rotation decreases. Additionally, the six stars analyzed here seem to fall into two categories, according to their spot flux deficit: those with ΔF spot > 0.005 and those with ΔF spot < 0.002.

Using synthetic disk-integrated reflectance spectra to constrain direct imaging sensitivity requirements for a Mars-like exoplanet

The 2020 Decadal Survey on Astronomy and Astrophysics 11https://doi.org/10.17226/26141. recommended the prioritization of a space-based telescope capable of directly characterizing Earth-like exoplanets in reflected light. The planned suite of instruments onboard such a mission are expected to provide disk-integrated spectra with moderate spectral resolution and signal-to-noise (SNR). Although the detection and characterization of Earth-like exoplanets remains the primary focus of such a mission, land planets with limited available water, such as Mars, may be much more common. Mars-like exoplanets, therefore, are an equally significant set of targets when investigating the diverse climatologies and potential habitability of other worlds, especially if our own Solar System is any indication of planetary diversity. In this study, we constrain the direct imaging sensitivity requirements for observing and characterizing Mars-like exoplanets with the goal of informing future telescope design and mission planning. Employing an instrument noise model simulating a coronagraph-equipped, space-based telescope, spatially- and spectrally-resolved synthetic observations of Mars are produced. We evaluate the direct imaging sensitivity requirements across a range of wavelengths, from the ultraviolet (UV) to near-infrared (near-IR), to enable the spectral characterization of key atmospheric and surface features from disk-integrated reflectance spectra. Detectability at a given SNR is assessed through optical wavelength integration times for a range of phase angles, host star spectral types, and levels of atmospheric dustiness. Our results indicate that a Decadal-recommended space telescope featuring an aperture of 6-m is likely only proficient in detecting Mars-like exoplanets around K-type stars located within a 10 parsec (pc) radius from Earth. Furthermore, we demonstrate that when integrating over visible and near-IR wavelengths, required exposure times to detect such a planet are reasonable, especially near full phase angles. In the context of upcoming and proposed observatories, such as the Habitable Exoplanet Observatory (HabEx) and Large UV/Optical/IR Surveyor (LUVOIR), our findings provide valuable insights into the direct imaging capabilities and optimal observational strategies needed for detecting and studying Mars-like exoplanets.

Periodic variable A-F spectral type stars in the southern TESS continuous viewing zone

Aims. Our primary objective is to accurately identify and classify the variability of A-F stars in the southern continuous viewing zone of the TESS satellite. The brightness limit was set to 10 mag to ensure the utmost reliability of our results and allow for spectroscopic follow-up observations using small telescopes. We aim to compare our findings with existing catalogues of variable stars. Methods. The light curves from TESS and their Fourier transform were used to manually classify stars in our sample. Cross-matching with other catalogues was performed to identify contaminants and false positives. Results. We have identified 1171 variable stars (51% of the sample). Among these variable stars, 67% have clear classifications, which includes δ Sct and γ Dor pulsating stars and their hybrids, rotationally variables, and eclipsing binaries. We have provided examples of the typical representatives of variable stars and discussed the ambiguous cases. We found 20 pairs of stars with the same frequencies and identified the correct source of the variations. Additionally, we found that the variations in 12 other stars are caused by contamination from the light of faint nearby large-amplitude variable stars. To compare our sample with other variable star catalogues, we have defined two parameters reflecting the agreement in identification of variable stars and their classification. This comparison reveals intriguing disagreements in classification ranging from 52 to 100%. However, if we assume that stars without specific types are only marked as variable, then the agreement is relatively good, ranging from 57 to 85% (disagreement 15–43%). We have demonstrated that the TESS classification is superior to the classification based on other photometric surveys. Conclusions. The classification of stellar variability is complex and requires careful consideration. Caution should be exercised when using catalogue classifications.

KIC 4150611: A quadruply eclipsing heptuple star system with a g-mode period-spacing pattern. Eclipse modelling of the triple and spectroscopic analysis.

KIC 4150611 is a high-order multiple composed of a triple system.\ It comprises: (1) a F1V primary (Aa) that is eclipsed on a 94.2d period by a tight 1.52d binary composed of two dim K/M dwarfs (Ab1 and Ab2), which also eclipse each other; (2) an 8.65d eccentric, eclipsing binary composed of two G stars (Ba and Bb); and (3) another faint eclipsing binary composed of two stars of unknown spectral type (Ca and Cb). In addition to its many eclipses, the system is an SB3 spectroscopic multiple (Aa, Ba, and Bb), and the primary (Aa) is a hybrid pulsator that exhibits high amplitude pressure and gravity modes. In aggregate, this richness in physics offers an excellent opportunity to obtain a precise physical characterisation of some of the stars in this system. In this work we aim to characterise the F1V primary by modelling its complex eclipse geometry and disentangled stellar spectra in preparation for follow-up work that will focus on its pulsations. We employed a novel photometric analysis of the complicated eclipse geometry of Aa to obtain the orbital and stellar properties of the triple. We acquired 51 TRES spectra at the Fred L. Whipple Observatory, calculating radial velocities and orbital elements of Aa (SB1) and the B binary (SB2). These spectra and radial velocities were used to perform spectral disentangling for Aa, Ba, and Bb. Spectral modelling was applied to the disentangled spectrum of Aa to obtain atmospheric properties. From our eclipse modelling we obtain precise stellar properties of the triple, including the mass ratios ($M_ Aa /(M_ Ab1 +M_ Ab2 Ab1 /M_ Ab2 the separation ratio Aab /a_ Ab1Ab2 0.01$), orbital periods Aab Ab1Ab2 and stellar radii ( R R R Via radial velocity fitting and spectral disentangling, we find orbital elements for Aa, Ba, and Bb that are in excellent agreement with each other and with previous results in the literature. Spectral modelling on the disentangled spectrum of Aa provides constraints on the effective temperature eff K), surface gravity (log$(g) = 4.14 0.18$ dex), micro-turbulent velocity micro rotation velocity ($v i = 127 and metallicity M/H

Host-star Properties of Hot, Warm, and Cold Jupiters in the Solar Neighborhood from Gaia Data Release 3: Clues to Formation Pathways

Giant planets exhibit diverse orbital properties, hinting at their distinct formation and dynamic histories. In this paper, using Gaia Data Release 3 (DR3), we investigate if and how the orbital properties of Jupiters are linked to their host star properties, particularly their metallicity and age. We obtain metallicities for main-sequence stars of spectral type F, G, and K, hosting hot, warm, and cold Jupiters with varying eccentricities. We compute the velocity dispersions of the host stars of these three groups using kinematic information from Gaia DR3 and obtain average ages using a velocity dispersion–age relation. We find that the host stars of hot Jupiters are relatively metal rich ([Fe/H] = 0.18 ± 0.13) and young (median age of 3.97 ± 0.51 Gyr) compared to the host stars of cold Jupiters in nearly circular orbits, which are relatively metal poor (0.03 ± 0.18) and older (median age of 6.07 ± 0.79 Gyr). The host stars of cold Jupiters in high-eccentricity orbits, on the other hand, show metallicities similar to those of the hosts of hot Jupiters, but are older, on average (median age of 6.25 ± 0.92 Gyr). The similarity in metallicity between the hosts of hot Jupiters and the hosts of cold Jupiters in high-eccentricity orbits supports high-eccentricity migration as the potential origin of hot Jupiters, with the latter serving as the progenitors of hot Jupiters. However, the average age difference between them suggests that the older hot Jupiters may have been engulfed by their host star over timescales ∼ 6 Gyr. This allows us to estimate the value of stellar tidal quality factor, Q*′∼106±1 .

Spectroscopic survey of faint planetary-nebula nuclei

We present spectroscopy of three hydrogen-deficient central stars of faint planetary nebulae, with effective temperatures (Teff) in excess of 100 000 K. The nucleus of RaMul 2 is a Population II Wolf-Rayet star of spectral type [WC], and the central stars of Abell 25 and StDr 138 are two new members of the PG1159 class. Our spectral analyses reveal that their atmospheres have a similar chemical composition. They are dominated by helium and carbon, which was probably caused by a late helium-shell flash. Coincidentally, the three stars have similar masses of about M = 0.53 M⊙ and hence form a post-asymptotic giant branch (AGB) evolutionary sequence of an initially early-K-type main sequence star with M = 0.8 M⊙. The central stars cover the period during which the luminosity fades from about 3000 to 250 L⊙ and the radius shrinks from about 0.15 to 0.03 R⊙. The concurrent increase of the surface gravity during this interval from log g = 5.8 to 7.2 causes the shutdown of the stellar wind from an initial mass-loss rate of log Ṁ/(M⊙ yr−1) = −6.4, as measured for the [WC] star. Along the contraction phase, we observe an increase in Teff from 112 000 K, marked by the [WC] star, to the maximum value of 140 000 K, and a subsequent cooling to 130 000 K, marked by the two PG1159 stars.

The Impact of Extended H2O Cross Sections on Temperate Anoxic Planet Atmospheres: Implications for Spectral Characterization of Habitable Worlds

JWST has created a new era of terrestrial exoplanet atmospheric characterization, and with it, the possibility to detect potential biosignature gases like CH4. Our interpretation of exoplanet atmospheric spectra, and the veracity of these interpretations, will be limited by our understanding of atmospheric processes and the accuracy of input modeling data. Molecular cross sections are essential inputs to these models. The photochemistry of temperate planets depends on photolysis reactions whose rates are governed by the dissociation cross sections of key molecules. H2O is one such molecule; the photolysis of H2O produces OH, a highly reactive and efficient sink for atmospheric trace gases. We investigate the photochemical effects of improved H2O cross sections on anoxic terrestrial planets as a function of host star spectral type and CH4 surface flux. Our results show that updated H2O cross sections, extended to wavelengths >200 nm, substantially impact the predicted abundances of trace gases destroyed by OH. The differences for anoxic terrestrial planets orbiting Sun-like host stars are greatest, showing changes of up to 3 orders of magnitude in surface CO levels, and over an order of magnitude in surface CH4 levels. These differences lead to observable changes in simulated planetary spectra, especially important in the context of future direct-imaging missions. In contrast, the atmospheres of planets orbiting M-dwarf stars are substantially less affected. Our results demonstrate a pressing need for refined dissociation cross-section data for H2O, where uncertainties remain, and other key molecules, especially at mid-UV wavelengths >200 nm.

Frequencies of Warm Debris Disks Based on Point Source Catalogs of Spitzer, WISE, and Gaia

More than a thousand warm debris disks have been detected as infrared excess at mid-infrared wavelengths, and their frequencies have been obtained for various spectral types of stars. However, the dependence of the frequencies on spectral type is still debated because the number of stars with significant and detectable infrared excess is limited. Herein, we present the largest systematic search for infrared excess using data from Gaia, WISE, and Spitzer. We identified 373, 485, and 255-reliable infrared excesses in the mid-infrared archival data at wavelengths of 12, 22, and 24 μm for WISE/W3, W4, and Spitzer/MIPS ch1, respectively. Although we confirmed that more massive stars tend to show higher frequencies of debris disks, these disk frequencies are relatively flat for both low- and intermediate-mass stars, with a jump at 7000 K for all three wavelengths. Assuming that bright, warm debris disks have lifetimes of a few to several hundred million years, the disk frequency can be understood as the ratio between the timescale and the upper limits of the sample ages. We also found that intermediate-mass stars with infrared excess tend to be bluer and fainter along the evolutionary track than those without, implying that massive stars hosting debris disks are relatively young, with an isochronal age of approximately 500 Myr. These tendencies are reasonably explained by a standard scenario in which debris disks are likely to be produced by collisions of planetesimals in the early stages of stellar evolution, such as the Late Heavy Bombardment.

The Impact-driven Atmospheric Loss of Super-Earths around Different Spectral Types of Host Stars

A planet’s mass loss is important for the its formation and evolution. The radius valley (RV) is believed to be triggered by evaporation-induced mass loss. As an alternative mechanism for RV, the mass loss of post-impact planets is thoroughly investigated in this work. The impact energy is converted to the planet’s internal energy, enhancing its core energy and accelerating mass loss and orbital migration. As the host star changes from K type to F type, the planet’s mass loss and orbital migration increase. When the initial gas-to-core-mass ratio is small, the migration efficiency for planets around K-type stars will increase, which helps to suppress mass loss and retain the planet’s mass and radius within a specific range. On the contrary, planets around more massive F-type stars experience more substantial mass loss, potentially leading to complete mass loss, and migrate to orbits with longer periods. Our calculation shows that planets around different spectral types of host stars give rise to an RV ranging from 1.3 to 2.0 R ⊕, consistent with the observed range of 1.3–2.6 R ⊕. Despite the presence of uncertain parameters, the planetesimal impact can promote the RV establishment for planets around host stars of different spectral types.

JWST/NIRCam Detection of the Fomalhaut C Debris Disk in Scattered Light

Observations of debris disks offer important insights into the formation and evolution of planetary systems. Though M dwarfs make up approximately 80% of nearby stars, very few M dwarf debris disks have been studied in detail—making it unclear how or if the information gleaned from studying debris disks around more massive stars extends to the more abundant M dwarf systems. We report the first scattered-light detection of the debris disk around the M4 star Fomalhaut C using JWST's Near Infrared Camera (NIRCam; 3.6 and 4.4 μm). This result adds to the prior sample of only four M dwarf debris disks with detections in scattered light and marks the latest spectral type and oldest star among them. The size and orientation of the disk in these data are generally consistent with the prior Atacama Large Millimeter/submillimeter Array submillimeter detection. Though no companions are identified, these data provide strong constraints on their presence—with sensitivity sufficient to recover sub-Saturn mass objects in the vicinity of the disk. This result illustrates the unique capability of JWST to uncover elusive M dwarf debris disks in scattered light and lays the groundwork for deeper studies of such objects in the 2–5 μm regime.

TOI-663: A newly discovered multi-planet system with three transiting mini-Neptunes orbiting an early M star

We present the detection of three exoplanets orbiting the early M dwarf TOI-663 (TIC 54962195; V = 13.7 mag, J = 10.4 mag, R★ = 0.512 ± 0.015 R⊙, M★ = 0.514 ± 0.012 M⊙, d = 64 pc). TOI-663 b, c, and d, with respective radii of 2.27 ± 0.10 R⊕, 2.26 ± 0.10 R⊕, and 1.92 ± 0.13 R⊕ and masses of 4.45 ± 0.65 M⊕, 3.65 ± 0.97 M⊕, and <5.2 M⊕ at 99%, are located just above the radius valley that separates rocky and volatile-rich exoplanets. The planet candidates are identified in two TESS sectors and are validated with ground-based photometric follow-up, precise radial-velocity measurements, and high-resolution imaging. We used the software package juliet to jointly model the photometric and radial-velocity datasets, with Gaussian processes applied to correct for systematics. The three planets discovered in the TOI-663 system are low-mass mini-Neptunes with radii significantly larger than those of rocky analogs, implying that volatiles, such as water, must predominate. In addition to this internal structure analysis, we also performed a dynamical analysis that confirmed the stability of the system. The three exoplanets in the TOI-663 system, similarly to other sub-Neptunes orbiting M dwarfs, have been found to have lower densities than planets of similar sizes orbiting stars of different spectral types.

A catalogue of low-mass X-ray binaries in the Galaxy: From the INTEGRAL to the Gaia era

Context. Low-mass X-ray binaries (LMXBs) are high-energy sources that require multi-wavelength follow-up campaigns to be fully characterised. New transients associated with LMXBs are regularly discovered, and previously known systems are often revisited by astronomers to constrain their intrinsic parameters. All of this information compiled into a catalogue may build a useful tool for subsequent studies on LMXBs and their population. Aims. We aim to provide an update on past LMXB catalogues dating back 16 yr and propose to the community a database on Galactic LMXBs with the most complete, manually curated set of parameters and their original references. On top of a fixed version accessible through Vizier, we propose hosting the catalogue independently on our GitHub collaboration, side-by-side with our previous catalogue on high-mass X-ray binaries. The database will be regularly updated based on new publications and community inputs. Methods. We built a working base by cross-matching previous LMXB catalogues and supplementing them with lists of hard X-ray sources detected over the past 20 yr. We compiled information from Simbad on LMXBs as a starting point for a thorough, manual search in the literature to retrieve important parameters that characterize LMXBs. We retrieved newly detected LMXBs and candidates directly from literature searches. Counterparts to these LMXBs are compiled from hard X-ray to infrared and radio domains. Every piece of information presented on the LMXBs is curated and backed by accurate references. Results. We present a catalogue of 339 Galactic LMXBs listing their coordinates, companion star spectral type, systemic radial velocity, component masses and compact object nature, the presence of type I X-ray bursts, as well as orbital data. Coordinates and identifiers of counterparts at various wavelengths are given, including 140 LMXBs detected in Gaia DR3.

Silicate Extinction Profile Based on the Stellar Spectrum by Spitzer/IRS

The 9.7 and 18 μm interstellar spectral features, arising from the Si–O stretching and O–Si–O bending modes of amorphous silicate dust, are the strongest extinction features in the infrared. Here we use the “pair method” to determine the silicate extinction profile by comparing the Spitzer/IRS spectra of 49 target stars with obvious extinction with those of unreddened stars of the same spectral type. The 9.7 μm extinction profile is determined from all the 49 stars and the 18 μm profile is determined from six stars. It is found that the profile has a peak wavelength at ∼9.2–9.8 and ∼18–22 μm, respectively. The peak wavelength of the 9.7 μm feature seems to become shorter for stars of late spectral types; meanwhile the FWHM seems irrelevant to the spectral type, which may be related to circumstellar silicate emission. The silicate optical depth at 9.7 μm, Δτ 9.7, mostly increases with the color excess in J − K S ( EJKS ). The mean ratio of the visual extinction to the 9.7 μm silicate absorption optical depth is A V /Δτ 9.7 ≈ 17.8, in close agreement with that of the solar-neighborhood diffuse interstellar medium. When EJKS>4 , this proportionality changes. The correlation coefficient between the peak wavelength and the FWHM of the 9.7 μm feature is 0.4, which indicates a positive correlation considering the uncertainties of the parameters. The method is compared with replacing the reference star by an atmospheric model spectral energy distribution and no significant difference is observed.

Time Variability of FUV Emission from Cool Stars on Multi-year Timescales

The physical and chemical properties of planetary atmospheres are affected by temporal evolution of ultraviolet (UV) radiation inputs from their host stars at all time scales. While studies of X-ray/UV flare properties and long-term stellar evolution of exoplanet host stars have provided new constraints regarding stellar inputs to exoplanetary systems, the UV temporal variability of cool stars on the timescale of stellar cycles remains largely unexplored. To address this gap in our understanding of the UV temporal variability of cool stars, we analyze far-ultraviolet (FUV) emission lines of ions that trace the chromosphere and transition region of nearby stars (C ii, Si iii, Si iv, and N v; formation temperatures ∼ 20–150 kK) using data from the Hubble Space Telescope (HST) and International Ultraviolet Explorer (IUE) archives spanning temporal baselines of months to years. We select 33 unique stars of spectral types F-M with observing campaigns spanning over a year, and create ionic light curves to evaluate the characteristic variability of cool stars on such timescales. Screening for large flare events, we observe that the relative variability of FUV light curves decreases with increasing stellar effective temperature, from 30% to 70% variability for M-type stars to <30% variability for F and G-type stars. We also observe a weak trend in the temporal variability with the Ca ii RHK′ stellar activity indicator, suggesting that stars with lower Ca ii activity exhibit a smaller range of FUV flux variability. Screening for data sets with optimal temporal spread, and a sufficient number of individual observations, we select 5 data sets for further periodicity analysis (HST α Centauri A, HST α Centauri B, IUE α Centauri B, IUE ϵ Eri, IUE ξ Boo). Various periodic structures within the FUV flux were detected, with most significant being a 79 days frequency present within the IUE observations of ξ Boo, with a significance of 6σ, and a periodic signal in the FUV observations of α Centauri B, for both HST and IUE measurements, at ≈210 days frequency with significance of 3σ and 3.7σ, respectively. Our results suggest that extreme ultraviolet flux from cool stars varies by less than a factor of two on decade timescales, significantly smaller than variations on flare or stellar evolutionary timescales.

A Uniform Analysis of Debris Disks with the Gemini Planet Imager. I. An Empirical Search for Perturbations from Planetary Companions in Polarized Light Images

The Gemini Planet Imager (GPI) has excelled in imaging debris disks in the near-infrared. The GPI Exoplanet Survey imaged 24 debris disks in polarized H-band light, while other programs observed half of these disks in polarized J and/or K1 bands. Using these data, we present a uniform analysis of the morphology of each disk to find asymmetries suggestive of perturbations, particularly those due to planet–disk interactions. The multiwavelength surface brightness, disk color, and geometry permit the identification of any asymmetries such as warps or disk offsets from the central star. We find that 19 of the disks in this sample exhibit asymmetries in surface brightness, disk color, disk geometry, or a combination of the three, suggesting that for this sample, perturbations, as seen in scattered light, are common. The relationship between these perturbations and potential planets in the system is discussed. We also explore correlations among stellar temperatures, ages, disk properties, and observed perturbations. We find significant trends between the vertical aspect ratio and the stellar temperature, disk radial extent, and the dust grain size distribution power law, q. We also confirm a trend between the disk color and stellar effective temperature, where the disk becomes increasingly red/neutral with increasing temperature. Such results have important implications for the evolution of debris disk systems around stars of various spectral types.

Thirty Bright High Velocity B, A, and F Stars that may have Late-type Companions

I found thirty high velocity stars that have large V − K values compared to standard stars of similar spectral types indicating the possible presence of late-type companion stars. All these thirty stars are relatively bright nearby stars with accurate Gaia DR3 parallaxes and radial velocities. There is hardly any relevant literature on these stars. There are 18 high galactic latitude stars in this sample. In order to further understand their chemical composition, evolutionary status, binary companions and how these stars acquired high radial velocities high resolution spectroscopy, radial velocity and photometric monitoring studies are very much needed.

Modelling stellar variability in archival HARPS data: I - Rotation and activity properties with multidimensional Gaussian processes

ABSTRACT Although instruments for measuring the radial velocities (RVs) of stars now routinely reach sub-metre per second accuracy, the detection of low-mass planets is still very challenging. The rotational modulation and evolution of spots and/or faculae can induce variations in the RVs at the level of a few m s–1 in Sun-like stars. To overcome this, a multidimensional Gaussian Process framework has been developed to model the stellar activity signal using spectroscopic activity indicators together with the RVs. A recently published computationally efficient implementation of this framework, S + LEAF 2, enables the rapid analysis of large samples of targets with sizeable data sets. In this work, we apply this framework to HARPS observations of 268 well-observed targets with precisely determined stellar parameters. Our long-term goal is to quantify the effectiveness of this framework to model and mitigate activity signals for stars of different spectral types and activity levels. In this first paper in the series, we initially focus on the activity indicators (S-index and Bisector Inverse Slope), and use them to (a) measure rotation periods for 49 slow rotators in our sample, (b) explore the impact of these results on the spin-down of middle-aged late F, G, and K stars, and (c) explore indirectly how the spot to facular ratio varies across our sample. Our results should provide valuable clues for planning future RV planet surveys such as the Terra Hunting Experiment or the PLATO ground-based follow-up observations programme, and help fine-tune current stellar structure and evolution models.

On the Influence of ‘‘Red Leak’’ of Light Filters on the Brightness Estimates of Stars of Late Spectral Types Illustrated by the Observations of Rapid Variability of Symbiotic Stars

On the Influence of ‘‘Red Leak’’ of Light Filters on the Brightness Estimates of Stars of Late Spectral Types Illustrated by the Observations of Rapid Variability of Symbiotic Stars

Spright: a probabilistic mass–density–radius relation for small planets

ABSTRACT We present spright, a python package that implements a fast and lightweight mass–density–radius relation for small planets. The relation represents the joint planetary radius and bulk density probability distribution as a mean posterior predictive distribution of an analytical three-component mixture model. The analytical model, in turn, represents the probability for the planetary bulk density as three generalized Student’s t-distributions with radius-dependent weights and means based on theoretical composition models. The approach is based on Bayesian inference and aims to overcome the rigidity of simple parametric mass–radius relations and the danger of overfitting of non-parametric mass–radius relations. The package includes a set of pre-trained and ready-to-use relations based on two M-dwarf catalogues, one catalogue containing stars of spectral types F, G, and K (FGK stars), and two theoretical composition models for water-rich planets. The inference of new models is easy and fast, and the package includes a command line tool that allows for coding-free use of the relation, including the creation of publication-quality plots. Additionally, we study whether the current mass and radius observations of small exoplanets support the presence of a population of water-rich planets positioned between rocky planets and sub-Neptunes. The study is based on Bayesian model comparison and shows somewhat strong support against the existence of a water-world population around M dwarfs. However, the results of the study depend on the chosen theoretical water-world density model. A more conclusive result requires a larger sample of precisely characterized planets and community consensus on a realistic water-world interior structure and atmospheric composition model.