List Of Stars Research Articles

Is the young star association ε Cha double?

The kinematics of the ε Cha young stellar association close to the Sun has been studied based on a list of candidate stars from the Dickson-Vandervelde work. The working sample consists of 26 stars with parallaxes, proper motions from the Gaia DR3 catalog and radial velocities taken from literary sources. The orbits of the stars back to the past were constructed, and the moment when the association had a minimum spatial size was determined, as well as an analysis of the dependencies of the velocities U, V, W on the coordinates x, y, z was carried out. It is shown that the initial sample is divided into two parts with different kinematic properties. The first sample included 9 stars. Based on the construction of the orbits of these 9 stars, an age estimate of t = 4.9 ± 0.8 million years was obtained. An expansion coefficient in the xz plane with the value Kxz = 135±19 km/s/kpc was also found for them, on the basis of which another age estimate t = 7.2 ± 1.0 million years was obtained. The second sample included 17 stars. The construction of their orbits gave an estimate of age t = 0.2 ± 0.3 million years, and based on the gradient dW/dz = 707 ± 248 km/s/kpc, a second estimate of their age t = 1.4 ± 0.5 million years was obtained. This suggests that the ε Cha association either consists of two groupings of different ages, or a younger one arose as a result of a recent outbreak of star formation within a common star system. The question of the gravitational connection of the groupings has not been considered in the framework of this work.

Long-period Ap stars discovered with TESS data: Cycles 3 and 4

One of the most challenging aspects of the Ap stars is the extreme differentiation of their rotation periods, which span more than five orders of magnitude. The physical origin of this differentiation remains poorly understood. The consideration of the most slowly rotating Ap stars represents a promising approach to gain insight into the processes responsible for the rotational braking to which the Ap stars are subject. However, historically, the study of these stars focused primarily on the most strongly magnetic among them. This bias introduced an ambiguity in the conclusions that could be drawn, as it did not allow the distinction between the rotational and magnetic effects, nor the investigation of possible correlations between rotational and magnetic properties. We previously showed that the identification of super-slowly rotating Ap (ssrAp) star candidates (defined as Ap stars that have rotation periods Prot > 50 d) through systematic exploitation of the available TESS photometric observations of Ap stars is an effective approach to build a sample devoid of magnetic bias. This approach rests on the presence of brightness spots on the surface of Ap stars that are not distributed symmetrically about their rotation axes and show long-term stability, hence are responsible for photometric variations with the stellar rotation period. In our previous analyses of TESS Cycle 1 and Cycle 2 data, we interpreted the Ap stars showing no such variability over the 27-d duration of a TESS sector as being ssrAp star candidates. Here, we applied the same approach to TESS Cycle 3 and Cycle 4 observations of Ap stars. We show, however, that two issues that had not been fully appreciated until now may lead to spurious identification of ssrAp star candidates. On the one hand, a considerable fraction of the Ap stars in the existing lists turn out to have erroneous or dubious spectral classifications. On the other hand, the TESS data processing may remove part of the variability signal, especially for stars with moderately long periods (20 d ≲ Prot ≲ 50 d). After critical evaluation of these effects, we report the identification of 25 new ssrAp star candidates and of eight stars with moderately long periods. Combining this list with the lists of ssrAp stars from Cycles 1 and 2 and with the list of ssrAp stars that were previously known but whose lack of variability was not detected in our study, we confirmed at a higher significance level the conclusions drawn in our earlier work. These include the lower rate of occurrence of super-slow rotation among weakly magnetic Ap stars than among strongly magnetic ones, the probable existence of a gap between ∼2 and ∼3 kG in the distribution of the magnetic field strengths of the ssrAp stars, and the much higher rate of occurrence of rapid oscillations in ssrAp stars than in the whole population of Ap stars. The next step to gain further understanding of the ssrAp stars will be to obtain high-resolution spectra of those for which such observations have not been made yet, to constrain their rotation velocities and their magnetic fields.

LAMOST J040901.83+329355.6 – a new Galactic star with Wolf–Rayet characteristics in the transitional stage from post-asymptotic giant branch to central star of a planetary nebula

ABSTRACT The similarity in physical conditions in the winds of low-mass post-asymptotic giant branch stars and evolved massive stars leads to the appearance of an interesting phenomenon of spectral mimicry. Because of this, the discovery of every new star with a Wolf–Rayet (WR) spectrum requires a special study of its evolutionary status before it can be included in the list of Galactic WR stars. A couple of years ago, LAMOST J040901.83+323955.6 (hereafter J0409+3239) was selected as a WR star in the LAMOST spectroscopic data base by machine-learning methods. In this work, we investigate its evolutionary status. After analysing the spatial location of J0409+3239 in the Galaxy and its position in the colour–magnitude diagram, we conclude that J0409+3239 is instead a low-mass object displayng the WR phenomenon. Its luminosity is $L*=1000~\rm L_\odot$ and its effective temperature is Teff = 40 000 K. Using new and archival photometric data, we detected irregular variability on time-scales from hours to tens of days with an amplitude of up to ~0.2 mag. A comparison of the spectrum obtained in 2022 with that from 2014 also shows evidence of spectral variability. The absence of a clearly detected circumstellar nebula prevents the classification of J0409+3239 as [WR], namely as the central star of a planetary nebula (CSPN). However, the position of J0409+3239 on the Hertzsprung–Russell diagram suggests that this object is a low-mass star caught in a rare transitional phase to CSPN. Estimation of the J0409+3239 mass based on evolutionary tracks shows that it is less than $0.9~\rm M_\odot$, and thus that the age of the Galaxy is barely sufficient for the star to have evolved to its current stage.

Doppler Constraints on Planetary Companions to Nearby Sun-like Stars: An Archival Radial Velocity Survey of Southern Targets for Proposed NASA Direct Imaging Missions* * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Directly imaging temperate rocky planets orbiting nearby, Sun-like stars with a 6 m class IR/O/UV space telescope, recently dubbed the Habitable Worlds Observatory, is a high-priority goal of the Astro2020 Decadal Survey. To prepare for future direct imaging (DI) surveys, the list of potential targets should be thoroughly vetted to maximize efficiency and scientific yield. We present an analysis of archival radial velocity data for southern stars from the NASA/NSF Extreme Precision Radial Velocity (EPRV) Working Group’s list of high-priority target stars for future DI missions (drawn from the HabEx, LUVOIR, and Starshade Rendezvous studies). For each star, we constrain the region of companion mass and period parameter space we are already sensitive to based on the observational baseline, sampling, and precision of the archival radial velocity (RV) data. Additionally, for some of the targets, we report new estimates of magnetic activity cycle periods, rotation periods, improved orbital parameters for previously known exoplanets, and new candidate planet signals that require further vetting or observations to confirm. Our results show that for many of these stars we are not yet sensitive to even Saturn-mass planets in the habitable zone, let alone smaller planets, highlighting the need for future EPRV vetting efforts before the launch of a DI mission. We present evidence that the candidate temperate super-Earth exoplanet HD 85512b is most likely due to the star’s rotation, and report an RV acceleration for δ Pav that supports the existence of a distant giant planet previously inferred from astrometry.

Constraining Nucleosynthesis in Neutrino-driven Winds: Observations, Simulations, and Nuclear Physics

A promising astrophysical site to produce the lighter heavy elements of the first r-process peak (Z = 38 − 47) is the moderately neutron-rich (0.4 < Y e < 0.5) neutrino-driven ejecta of explosive environments, such as core-collapse supernovae and neutron star mergers, where the weak r-process operates. This nucleosynthesis exhibits uncertainties from the absence of experimental data from (α, xn) reactions on neutron-rich nuclei, which are currently based on statistical model estimates. In this work, we report on a new study of the nuclear reaction impact using a Monte Carlo approach and improved (α, xn) rates based on the Atomki-V2 α optical model potential. We compare our results with observations from an up-to-date list of metal-poor stars with [Fe/H] < −1.5 to find conditions of the neutrino-driven wind where the lighter heavy elements can be synthesized. We identified a list of (α, xn) reaction rates that affect key elemental ratios in different astrophysical conditions. Our study aims to motivate more nuclear physics experiments on (α, xn) reactions using the current and new generation of radioactive beam facilities and also more observational studies of metal-poor stars.

Gaia EDR3 comparative study of protoplanetary disk fractions in young stellar clusters

Context. The lifetime of protoplanetary disks around young stars limits the timescale of planet formation. A disk dissipation timescale ≤10 Myr was inferred from surveys that count the relative number of stars with disks – the disk fraction – in young stellar clusters with different ages. However, most previous surveys focused on the compact region within ∼2 pc of the clusters’ centers, for which the disk fraction information about the outer part is practically absent. Aims. We aim to test if disk fraction estimates change when inferred from an extended region around the clusters’ centers. Methods.Gaia EDR3 data and a best-suited, Virtual Observatory (VO)-based tool – Clusterix – are used to identify member stars for a representative sample of 19 young stellar clusters considering two concentric fields of view (FOVs) with radii of ∼20 pc and ∼2 pc. Inner-disk fractions associated with each FOV are identically derived from 2MASS color-color diagrams and compared to each other. Results. Although the density of members is smaller in the periphery, the absolute number of member stars is typically ∼5 times larger at distances farther than ∼2 pc from the clusters’ centers. In turn, our analysis reveals that the inner disk fractions inferred from the compact and the extended regions are equal within ∼±10%. A list of member and disk stars identified in each cluster is provided and stored in a VO-compliant archive, along with their membership probabilities, angular distances to the center, and Gaia and near-infrared data. Averaged values and plots that characterize the whole clusters are also provided, including Hertzsprung-Russell diagrams based on Gaia colors and absolute magnitudes for the sources with known extinction. Conclusions. Our results cover the largest fields ever probed when dealing with disk fractions for all clusters analyzed, and imply that their complete characterization requires the use of wide FOVs. However, the comparative study does not support a previous hypothesis that disk fractions should be significantly larger when extended regions are considered. The resulting database is a benchmark for future detailed studies of young clusters, whose disk fractions must be accurately determined by using multiwavelength analysis potentially combined with data from upcoming Gaia releases.

LAMOST J045019.27 + 394758.7, with peculiar abundances of N, Na, V, Zn, is possibly a Sculptor dwarf galaxy escapee

ABSTRACT We present the results of the high-resolution (R ∼ 60 000) spectroscopic analysis of the star LAMOSTJ045019.27 + 394758.7 (hereafter J045) from the list of carbon stars of LAMOST DR2. From our analysis, we find that J045 does not exhibit the spectral characteristics of carbon stars. It is found to be a metal-poor ([Fe/H] = −1.05) giant that shows very unusual elemental abundances, particularly for N, Na, V, and Zn. J045 shows α-elements (Mg, Si, Ca) with near-solar values (&amp;lt;[α/Fe]&amp;gt; = 0.09) in contrast to Galactic stars that show [α/Fe] in the range 0.2–0.3 dex. In J045, Sc and Ti are under abundant with [X/Fe] ≤ −0.25. Vanadium gives [V/Fe] = 0.51 and zinc is under-abundant with [Zn/Fe] = −0.62. The object exhibits near-solar abundances for Sr, Y, Ba, Pr, and Sm. The La is marginally enhanced, and Ce and Nd are marginally under-abundant in J045. With [Ba/Eu] = −0.38, the object falls into the category of neutron-capture rich r-I stars. The estimated abundances of various elements show that the observed abundance pattern is not compatible with the abundances characteristic of Galactic metal-poor stars but matches quite closely with the abundance pattern of Sculptor Dwarf galaxy stars of similar metallicity. Based on the above observational evidences, we suggest that the object is a possible Sculptor Dwarf Galaxy escapee.

Investigating Galactic binary cluster candidates with Gaia EDR3

ABSTRACT A number of stellar open cluster (OC) pairs in the Milky Way occupy similar positions in the phase space (coordinates, parallax, and proper motions) and therefore may constitute physically interacting systems. The characterization of such objects based on observational data is a fundamental step towards a proper understanding of their physical status and to investigate cluster pair formation in the Galaxy. In this work, we employed the Gaia EDR3 data to investigate a set of 16 OCs distributed as 7 stellar aggregates. We determined structural parameters and applied a decontamination technique that allowed us to obtain unambiguous lists of member stars. The studied OCs span Galactocentric distances and ages in the ranges of $7\lesssim \, R_\mathrm{ G}(\textrm {kpc})\lesssim 11$ and $7.3\le \textrm {log}\, t\le 9.2$. Eight OCs were found to constitute four gravitationally bound pairs (NGC 5617–Trumpler 22, Collinder 394–NGC 6716, Ruprecht 100–Ruprecht 101, and NGC 659–NGC 663, the latter being a dynamically unevolved binary) and other four clusters constitute two interacting, but gravitationally unbound, pairs (King 16–Berkeley 4 and NGC 2383–NGC 2384, the latter being a dissolving OC). Other four OCs (Dias 1, Pismis 19, Czernik 20, and NGC 1857) seem not associated with any stellar aggregates. Apparently, clusters within bound and dynamically evolved pairs tend to present ratios of half-light to tidal radius larger than single clusters located at similar RG, suggesting that mutual tidal interactions may possibly affect their structural parameters. Unbound or dynamically unevolved systems seem to present less noticeable signature of tidal forces on their structure. Moreover, the core radius seems more importantly correlated with the clusters’ internal dynamical relaxation process.

Determination of dynamical ages of open clusters through the A+ parameter – I

ABSTRACT The sedimentation level of blue straggler stars (BSS) has been shown to be a great tool to investigate the dynamical states of globular clusters (GCs). The area enclosed between the cumulative radial distributions of BSS and a reference population up to the half-mass radius of the clusters, $A^+_{\mathrm{rh}}$, is known to be a measure of the sedimentation of BSS in GCs. In this work, we calculate $A^+_{\mathrm{rh}}$ for 11 open clusters (OCs) using a combined list of main-sequence turn-off stars, sub-giant branch stars, and red giant branch stars as reference population. The BSS, the reference populations, and the cluster members are identified using the proper motions and parallaxes from the Gaia DR2 data. In a subset of clusters, the BSS are confirmed cluster members on the basis of radial velocity information available in the literature. Using the Pearson and Spearman rank correlation coefficients, we find weak correlations between the estimated values of $A^+_{\mathrm{rh}}$ and other markers of dynamical ages of the clusters, i.e. the number of central relaxations a cluster has experienced since its formation, and the structural parameters of the clusters. Based on statistical tests, we find that these correlations are similar to the corresponding correlations among the less evolved GCs, albeit within large errors.

On the weak 2-coloring number of planar graphs

For a graph G=(V,E), a total ordering L on V, and a vertex v∈V, let Wcol2[G,L,v] be the set of vertices w∈V for which there is a path from v to w whose length is 0, 1 or 2 and whose L-least vertex is w. The weak 2-coloring number wcol2(G) of G is the least k such that there is a total ordering L on V with |Wcol2[G,L,v]|≤k for all vertices v∈V. We improve the known upper bound on the weak 2-coloring number of planar graphs from 28 to 23. As the weak 2-coloring number is the best known upper bound on the star list chromatic number of planar graphs, this bound is also improved.

VVV survey near-infrared colour catalogue of known variable stars

Context. The Vista Variables in the Via Lactea (VVV) near-infrared variability survey explores some of the most complex regions of the Milky Way bulge and disk in terms of high extinction and high crowding. Aims. We add a new wavelength dimension to the optical information available at the American Association of Variable Star Observers International Variable Star Index (VSX-AAVSO) catalogue to test the VVV survey near-infrared photometry to better characterise these objects. Methods. We cross-matched the VVV and the VSX-AAVSO catalogues along with Gaia Data Release 2 photometry and parallax. Results. We present a catalogue that includes accurate individual coordinates, near-infrared magnitudes (ZYJHKs), extinctions AKs, and distances based on Gaia parallaxes. We also show the near-infrared CMDs and spatial distributions for the different VSX types of variable stars, including important distance indicators, such as RR Lyrae, Cepheids, and Miras. By analysing the photometric flags in our catalogue, we found that about 20% of the stars with measured and verified variability are flagged as non-stellar sources, even when they are outside of the saturation and/or noise regimes. Additionally, we pair-matched our sample with the VIVA catalogue and found that more than half of our sources are missing from the VVV variability list, mostly due to observations with low signal-to-noise ratio or photometric problems with a low percentage due to failures in the selection process. Conclusions. Our results suggest that the current knowledge of the variability in the Galaxy is biased to nearby stars with low extinction. The present catalogue also provides the groundwork for characterising the results of future large variability surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time in the highly crowded and reddened regions of the Galactic plane, as well as follow-up campaigns for characterising specific types of variables. The analysis of the incorrectly flagged stars can be used to improve the photometric classification of the VVV data, allowing us to expand the amount of data considered useful for science purposes. In addition, we provide a list of stars that are missed by the VIVA procedures for which the observations are good and which were missed due to some failure in the VIVA selection process.

Which stars can see Earth as a transiting exoplanet?

ABSTRACT Transit observations have found the majority of exoplanets to date. Also spectroscopic observations of transits and eclipses are the most commonly used tool to characterize exoplanet atmospheres and will be used in the search for life. However, an exoplanet’s orbit must be aligned with our line of sight to observe a transit. Here, we ask, from which stellar vantage points would a distant observer be able to search for life on Earth in the same way? We use the TESS Input Catalog and data from Gaia DR2 to identify the closest stars that could see Earth as a transiting exoplanet: We identify 1004 main-sequence stars within 100 parsecs, of which 508 guarantee a minimum 10-h long observation of Earth’s transit. Our star list consists of about 77 percent M-type, 12 percent K-type, 6 percent G-type, 4 percent F-type stars, and 1 percent A-type stars close to the ecliptic. SETI searches like the Breakthrough Listen Initiative are already focusing on this part of the sky. Our catalogue now provides a target list for this search. As part of the extended mission, NASA’s TESS will also search for transiting planets in the ecliptic to find planets that could already have found life on our transiting Earth .

TOI 694b and TIC 220568520b: Two Low-mass Companions near the Hydrogen-burning Mass Limit Orbiting Sun-like Stars

Abstract We report the discovery of TOI 694 b and TIC 220568520 b, two low-mass stellar companions in eccentric orbits around metal-rich Sun-like stars, first detected by the Transiting Exoplanet Survey Satellite (TESS). TOI 694 b has an orbital period of 48.05131 ± 0.00019 days and eccentricity of 0.51946 ± 0.00081, and we derive a mass of 89.0 ± 5.3 (0.0849 ± 0.0051 ) and radius of 1.111 ± 0.017 (0.1142 ± 0.0017 ). TIC 220568520 b has an orbital period of 18.55769 ± 0.00039 days and eccentricity of 0.0964 ± 0.0032, and we derive a mass of 107.2 ± 5.2 (0.1023 ± 0.0050 ) and radius of 1.248 ± 0.018 (0.1282 ± 0.0019 ). Both binary companions lie close to and above the hydrogen-burning mass threshold that separates brown dwarfs and the lowest-mass stars, with TOI 694 b being 2σ above the canonical mass threshold of 0.075 . The relatively long periods of the systems mean that the magnetic fields of the low-mass companions are not expected to inhibit convection and inflate the radius, which according to one leading theory is common in similar objects residing in short-period tidally synchronized binary systems. Indeed we do not find radius inflation for these two objects when compared to theoretical isochrones. These two new objects add to the short but growing list of low-mass stars with well-measured masses and radii, and highlight the potential of the TESS mission for detecting such rare objects orbiting bright stars.

Programa computacional científico para a elaboração automática de listas de estrelas para astronomia de posição (LEDAP): revisão dos conceitos e exemplo de aplicação

É apresentado o LEDAP, programa computacional científico que elabora automaticamente listas de estrelas para a determinação astronômica de precisão da latitude (método de Sterneck), longitude (método das distâncias zenitais absolutas) e azimute (método das estrelas em circum-elongação). As aplicações das listas nas práticas de Astronomia de Posição possibilitam a rápida obtenção de coordenadas astronômicas e respectivos desvios-padrões. O conhecimento das coordenadas astronômicas e geodésicas (juntamente com as precisões) de um ponto permite o observador estimar pelo método astrogeodésico as componentes meridiana (ξ), 1° vertical (η) e o desvio da vertical (i), bem como, os respectivos desvios-padrões por propagação de covariâncias. Neste trabalho, a partir do uso de um teodolito de leitura direta de 1” e de um receptor de dupla frequência foram obtidas as coordenadas astronômicas e geodésicas (posicionamento relativo estático) de um pilar de concreto localizado na UNESP, câmpus Presidente Prudente/SP, bem como, as componentes e o desvio, sendo ξ = 3,3339 ± 3,3323”, η = –54,8849 ± 4,5255” e i = 54,9861 ± 4,5217”. Verificou-se que devido às precisões das coordenadas astronômicas serem inferiores às geodésicas, as precisões das componentes e do desvio foram da ordem de 4,5”, independentemente do método de posicionamento por satélites utilizado, com exceção do Posicionamento por Ponto Simples (PPS) que degradou as estimativas.

A surprise in the updated list of stellar perturbers of long-period comet motion

Context. The second Gaia data release (Gaia DR2) provided us with the precise five-parameter astrometry for 1.3 billion of sources. As stars passing close to the Solar System are thought to influence the dynamical history of long-period comets, we update and extend the list of stars that could potentially perturb the motion of these comets. Aims. We announce a publicly available database containing an up-to-date list of stars and stellar systems potentially perturbing the motion of long-period comets. We add new objects and revise previously published lists. Special emphasis is placed on stellar systems. A discussion of mass estimation is included. Methods. Using the astrometry, preferably from Gaia DR2, augmented with data from other sources, we calculate nominal spatial positions and velocities for each star. To filter studied objects on the basis of their nominal minimum heliocentric distances we numerically integrate the motion of stars under the Galactic potential and their mutual interactions. Results. We announce the updated list of stellar perturbers of cometary motion, including the masses of perturbers along with the publicly available database interface. These data are ready to be used with the observed long-period comets orbits to study an individual influence of a whole sample of perturbers, or specific stars, on a dynamical past or future of a specific comet. New potential perturbers were added; there are 138 more than in the previously published sources. Conclusions. We demonstrate that a new set of prospective perturbers is an important tool in studies of cometary dynamics. The use of our data changes the results of the past and future cometary motion analysis. We point out a puzzling object in our list, star ALS 9243. The Gaia DR2 astrometry suggests a very close encounter of this star with the Sun; however, its astrophysical parameters result in a completely different current distance of ALS 9243 and its high mass.

Searching for exoplanets by HEPS II. detecting earth-like planets in habitable zone around planet hosts within 30 pc

HEPS (Habitable ExoPlanet Survey) is a planning astrometry satellite that aims to find Earth-like planets in the solar neighbourhood. In this paper, we selected 140 planet harboring stars within 30 pc of the solar system to be potential targets for HEPS. We calculate the detection probability of the planet in habitable zone (HZ) for each system using the simulated data of astrometry measurements. For those host stars without planets in HZ, we inject an additional planet of 10 M⊕ in their HZs and check the stability of the systems. Considering five observation modes of different sampling cadence and total observation time, we obtain a table containing the total detection probability of the planets in HZs for all of the 140 selected systems. This paper provides a potential ranked list of target stars for HEPS, or other astrometric mission to detect Earth-like planets in the future. We also calculate an empirical fitted expression of the detection probability as a function of both sampling cadence and total observation time. We conclude a quantitative method to estimate the detection probability for certain planet hosts and observation modes via the empirical expression. We show the minimum requirements of both sampling cadence and observation time for Proxima Centauri, HD 189733 and HD 102365, if the detection probability of habitable-zone planets of these three systems needs to be 90%.

Masses and Implications for Ages of Low-mass Pre-main-sequence Stars in Taurus and Ophiuchus

The accuracy of masses of pre-main sequence (PMS) stars derived from their locations on the Hertzsprung-Russell Diagram (HRD) can be tested by comparison with accurate and precise masses determined independently. We present 29 single stars in the Taurus star-forming region (SFR) and 3 in the Ophiuchus SFR with masses measured dynamically to a precision of at least $10 \%$. Our results include 9 updated mass determinations and 3 that have not had their dynamical masses published before. This list of stars with fundamental, dynamical masses, M$_{dyn}$, is drawn from a larger list of 39 targets in the Taurus SFR and 6 in the Ophiuchus SFR. Placing the stars with accurate and precise dynamical masses on HRDs that do not include internal magnetic fields underestimates the mass compared to M$_{dyn}$ by about $30 \%$. Placing them on an HRD that does include magnetic fields yields mass estimates in much better agreement with M$_{dyn}$, with an average difference between M$_{dyn}$ and the estimated track mass of $0.01\pm0.02$~\msun. The ages of the stars, 3--10 MY on tracks that include magnetic fields, is older than the 1--3 MY indicated by the non-magnetic models. The older ages of T Tauri stars predicted by the magnetic models increase the time available for evolution of their disks and formation of the giant gas exoplanets. The agreement between our M$_{dyn}$ values and the masses on the magnetic field tracks provides indirect support for these older ages.

A comprehensive taxonomic list of brittle stars (Echinodermata: Ophiuroidea)from submarine caves of the Ryukyu Islands, southwestern Japan, with a description of a rare species, Dougaloplus echinatus (Amphiuridae).

The ophiuroid species listed were collected by benthic faunal surveys from 2016 to 2018 in submarine caves of the Ryukyu Islands, southwestern Japan. The material includes 20 species from 8 families, Amphiuridae, Ophiocomidae, Ophiodermatidae, Ophiolepididae, Ophioleucidae, Ophiomyxidae, Ophionereididae and Ophiotrichidae. This is the first comprehensive report of submarine cave-dwelling ophiuroids from Japanese waters. Also provided is a redescription of a rare species, Dougaloplus echinatus (Ljungman, 1867), with a detailed description of its ossicle morphology. The species has previously been reported from Brazil, Australia, Eastern Indian Ocean to Southern China, in 11-118 m depth, and this is the first record of D. echinatus from Japanese waters. A brief discussion of the scarcity of submarine cave systems, and the need for their conservation, is provided.

The Asteroseismic Target List for Solar-like Oscillators Observed in 2 minute Cadence with the Transiting Exoplanet Survey Satellite

Abstract We present the target list of solar-type stars to be observed in short-cadence (2 minute) for asteroseismology by the NASA Transiting Exoplanet Survey Satellite (TESS) during its 2 year nominal survey mission. The solar-like Asteroseismic Target List (ATL) is comprised of bright, cool main-sequence and subgiant stars and forms part of the larger target list of the TESS Asteroseismic Science Consortium. The ATL uses the Gaia Data Release 2 and the Extended Hipparcos Compilation (XHIP) to derive fundamental stellar properties, to calculate detection probabilities, and to produce a rank-ordered target list. We provide a detailed description of how the ATL was produced and calculate expected yields for solar-like oscillators based on the nominal photometric performance by TESS. We also provide a publicly available source code that can be used to reproduce the ATL, thereby enabling comparisons of asteroseismic results from TESS with predictions from synthetic stellar populations.

Physical Properties of Galactic RV Tauri Stars from Gaia DR2 Data

Abstract We present the first period–luminosity and period–radius relation of Galactic RV Tauri variable stars. We have surveyed the literature for all variable stars belonging to this class and compiled the full set of their photometric and spectroscopic measurements. We crossmatched the final list of stars with the Gaia Data Release 2 database and took the parallaxes, G-band magnitudes, and effective temperatures to calculate the distances, luminosities, and radii using a probabilistic approach. As it turned out, the sample was very contaminated, and thus we restricted our study to those objects for which the RV Tau nature was securely confirmed. We found that several stars are located outside the red edge of the classical instability strip, which implies a wider pulsational region for RV Tau stars. The period–luminosity relation of galactic RV Tauri stars is steeper than that of the shorter-period Type II Cepheids, in agreement with previous results obtained for the Magellanic Clouds and globular clusters. The median masses of RVa and RVb stars were calculated to be 0.45–0.52 M ⊙ and 0.83 M ⊙, respectively.