Abstract
Circumbinary disks are common around post-asymptotic giant branch (post-AGB) stars with a stellar companion on orbital timescales of a few 100 to few 1000 days. The presence of a disk is ...usually inferred from the system’s spectral energy distribution and confirmed, for a sub-sample, by interferometric observations. We used the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on the Very Large Telescope to obtain extreme adaptive optics assisted scattered light images of the post-AGB binary system AR Puppis. Data have been obtained in the
V
,
I
, and
H
bands. Our observations have produced the first resolved images of AR Puppis’s circumbinary disk and confirm its edge-on orientation. In our high-angular-resolution and high-dynamic-range images we identify several structural components such as a dark mid-plane, the disk surface, and arc-like features. We discuss the nature of these components and use complementary photometric monitoring to relate them to the orbital phase of the binary system. Because the star is completely obscured by the disk at visible wavelengths, we conclude that the long-term photometric variability of the system must be caused by variable scattering, not extinction, of starlight by the disk over the binary orbit. Finally, we discuss how the short disk lifetimes and fast evolution of the host stars compared to the ages at which protoplanetary disks are typically observed make systems like AR Puppis valuable extreme laboratories to study circumstellar disk evolution and constrain the timescale of dust grain growth during the planet formation process.
Classical barium stars are binary systems which consist of a late-type giant enriched in carbon and slow neutron capture (s-process) elements and an evolved white dwarf (WD) that is invisible at ...optical wavelengths. The youngest observed barium stars are surrounded by planetary nebulae (PNe), ejected soon after the wind accretion of polluted material when the WD was in its preceding asymptotic giant branch (AGB) phase. Such systems are rare but powerful laboratories for studying AGB nucleosynthesis as we can measure the chemical abundances of both the polluted star and the nebula ejected by the polluter. Here, we present evidence for a barium star in the PN Hen 2-39 (PN G283.8-04.2) as one of only a few known systems. The polluted giant is very similar to that found in WeBo 1 (PN G135.6+01.0). It is a cool (Teff = 4250 ± 150 K) giant enhanced in carbon (C/H = 0.42 ± 0.02 dex) and barium (Ba/Fe = 1.50 ± 0.25 dex). A spectral type of C-R3 C24 nominally places Hen 2-39 amongst the peculiar early R-type carbon stars; however, the barium enhancement and likely binary status mean that it is more likely to be a barium star with similar properties, rather than a true member of this class. An AGB star model of initial mass 1.8 M... and a relatively large carbon pocket size can reproduce the observed abundances well, provided mass is transferred in a highly conservative way from the AGB star to the polluted star (e.g. wind Roche lobe overflow). It also shows signs of chromospheric activity and photometric variability with a possible rotation period of ~5.5 d likely induced by wind accretion. The nebula exhibits an apparent ring morphology in keeping with the other PNe around barium stars (WeBo 1 and A 70) and shows a high degree of ionization implying the presence of an invisible hot pre-WD companion that will require confirmation with UV observations. In contrast to A 70, the nebular chemical abundance pattern is consistent with non-Type I PNe, in keeping with the trend found from nebular s-process studies that non-Type I PNe are more likely to be s-process enhanced. (ProQuest: ... denotes formulae/symbols omitted.)
Transmission spectroscopy is an important technique to probe the atmospheres of exoplanets. With the advent of the Transiting Exoplanet Survey Satellite (TESS) and, in the future, of the PLAnetary ...Transits and Oscillations of stars (PLATO), more and more transiting planets around bright stars will be found and the observing time of current large telescopes used to apply these techniques will not suffice. We demonstrate here that 2-m class telescopes equipped with spectrographs with high resolving power may be used for a certain number of potential targets. We obtained a timeseries of high-resolution Fiber-fed Extended Range Optical Spectrograph (FEROS) spectra at the 2.2-m telescope at La Silla of the very hot-Jupiter hosting planet, WASP-18b, and show that our upper limit is consistent with the expectations. This is the first analysis of its kind using 2-m class telescopes, and it serves to highlight their potential. In this context, we then proceed to discuss the suitability of this class of telescopes for the upcoming flood of scientifically interesting targets from the TESS space mission, and propose a methodology to select the most promising targets. This is of particular significance given that observing time on 2-m class telescopes is more readily available than on large 8-m class facilities.
Abstract
We present a study based on Gaia DR2 of the population of blue straggler stars in the open clusters Trumpler 5, Trumpler 20, and NGC 2477. All candidates were selected according to their ...position in the color–magnitude diagram, their proper motion components, and their parallax. We also looked for yellow stragglers, i.e., possible evolved blue stragglers. We found that Trumpler 5 hosts a large blue straggler star population, which allowed us to analyze their radial distribution as a probe of the cluster’s dynamical status. The blue straggler star distribution was compared with that of red giant branch stars to evaluate mass segregation. Our results indicate that blue straggler stars are not more centrally concentrated than red giant branch stars stars in any of the clusters. The radial distribution of blue straggler stars in Trumpler 5 is flat. Additionally, using a multi-epoch radial velocity survey conducted with the high-resolution spectrograph FLAMES/GIRAFFE at the Very Large Telescope, we measured the radial velocities of a sample of stragglers to compare with the mean radial velocity and velocity dispersion of the clusters. Based on the radial velocity variations for different epochs, we roughly classified these stars as possible close or long-period binaries.
PENELLOPE Frasca, A.; Boffin, H. M. J.; Manara, C. F. ...
Astronomy and astrophysics (Berlin),
12/2021, Letnik:
656
Journal Article
Recenzirano
Odprti dostop
We present the results of our study of the close pre-main sequence spectroscopic binary CVSO 104 in Ori OB1, based on data obtained within the PENELLOPE legacy program. We derive, for the first time, ...the orbital elements of the system and the stellar parameters of the two components. The system is composed of two early M-type stars and has an orbital period of about five days and a mass ratio of 0.92, but contrary to expectations, it does not appear to have a tertiary companion. Both components have been (quasi-)synchronized, but the orbit is still very eccentric. The spectral energy distribution clearly displays a significant infrared excess that is compatible with a circumbinary disk. The analysis of He
I
and Balmer line profiles, after the removal of the composite photospheric spectrum, reveals that both components are accreting at a similar level. We also observe excess emission in H
α
and H
β
, which appears redshifted or blueshifted by more than 100 km s
−1
with respect to the mass center of the system, depending on the orbital phase. This additional emission could be connected with accretion structures, such as funnels of matter from the circumbinary disk. We also analyze the optical companion located at about 2.″4 from the spectroscopic binary. This companion, which we named CVSO 104 B, turns out to be a background Sun-like star that is not physically associated with the PMS system and does not belong to Ori OB1.
LoTr 1 is a planetary nebula thought to contain an intermediate-period binary central star system (that is, a system with an orbital period, P, between 100 and, say, 1500 d). The system shows the ...signature of a K type, rapidly rotating giant and most likely constitutes an accretion-induced post-mass-transfer system similar to other PNe, such as LoTr 5, WeBo 1 and A70. Such systems represent rare opportunities to further the investigation into the formation of barium stars and intermediate-period post-asymptotic giant branch systems - a formation process still far from being understood. Here, we present the first detailed analyses of both the central star system and the surrounding nebula of LoTr 1 using a combination of spectra obtained with Very Large Telescope-Focal Reducer and low dispersion Spectrograph, Anglo-Australian Telescope-UCL Coudé Echelle Spectrograph and New Technology Telescope-European Southern Observatory Multi-Mode Instrument, as well as SuperWASP (Wide Angle Search for Planets) photometry. We confirm the binary nature of the central star of LoTr 1 that consists of a K1 III giant and a hot white dwarf. The cool giant does not present any sign of s-process enhancement but is shown to have a rotation period of 6.4 d, which is a possible sign of mass accretion. LoTr 1 also presents broad double-peaked Hα emission lines, whose origin is still unclear. The nebula of LoTr 1 consists in two slightly elongated shells, with ages of 17 000 and 35 000 yr, respectively, and with different orientations. As such, LoTr 1 present a very different nebular morphology than A70 and WeBo 1, which may be an indication of difference in the mass-transfer episodes.
We present a detailed photometric study of the central star system of the planetary nebula Hen 2-11, selected for study because of its low-ionisation filaments and bipolar morphology – traits which ...have been strongly linked with central star binarity. Photometric monitoring with NTT-EFOSC2 reveals a highly irradiated, double-eclipsing, post-common-envelope system with a period of 0.609 d. Modelling of the lightcurve indicates that the nebular progenitor is extremely hot, while the secondary in the system is probably a K-type main sequence star. The chemical composition of the nebula is analysed, showing Hen 2-11 to be a medium-excitation non-Type i nebula. A simple photoionisation model is constructed determining abundance ratios of C/O and N/O which would be consistent with the common-envelope cutting short the AGB evolution of the nebular progenitor. The detection of a post-common-envelope binary system at the heart of Hen 2-11 further strengthens the link between binary progeny and the formation of axisymmetric planetary nebulae with patterns of low-ionisation filaments, clearly demonstrating their use as morphological indicators of central star binarity.
Aims. We aim at obtaining near-infrared photometry and deriving the mass, age, temperature, and surface gravity of WISE J085510.74–071442.5 (J0855–0714), which is the coolest object beyond the solar ...system currently known. Methods. We used publicly available data from the archives of the Hubble Space Telescope (HST) and the Very Large Telescope (VLT) to determine the emission of this source at 1.153 μm (F110W) and 1.575 μm (CH4-off). J0855–0714 was detected at both wavelengths with a signal-to-noise ratio of ≈10 (F110W) and ≈4 (CH4-off) at the peak of the corresponding point-spread-functions. Results. This is the first detection of J0855–0714 in the H-band wavelengths. We measured 26.31 ± 0.10 and 23.22 ± 0.35 mag in F110W and CH4-off (Vega system). J0855–0714 remains unresolved in the HST images that have a spatial resolution of 0.22′′. Companions at separations of 0.5 AU (similar mass and brightness) and at ~1 AU (≈1 mag fainter in the F110W filter) are discarded. By combining the new data with published photometry, including non-detections, we build the spectral energy distribution of J0855–0714 from 0.89 through 22.09 μm, and contrast it against current solar-metallicity models of planetary atmospheres. We determine that the best spectral fit yields a temperature of 225–250 K, a bolometric luminosity of log L/L⊙ = −8.57, and a high surface gravity of log g = 5.0 (cm s-2), which suggests an old age although a gravity this high is not fully compatible with evolutionary models. After comparing our data with the cooling theory for brown dwarfs and planets, we infer a mass in the interval 2–10 MJup for ages of 1–12 Gyr and high atmospheric gravities of log g ⪆ 3.5 (cm s-2). If it had the age of the Sun, J0855–0714 would be a ≈5-MJup free-floating planetary-mass object. Conclusions. J0855–0714 meets the mass values previously determined for free-floating planetary-mass objects discovered in star-forming regions and young stellar clusters. Based on extrapolations of the substellar mass functions of young clusters to the field, as many J0855–0714-like objects as M5–L2 stars may be expected to populate the solar neighborhood.
ABSTRACT
We present the confirmation and characterization of three hot Jupiters, TOI-1181b, TOI-1516b, and TOI-2046b, discovered by the TESS space mission. The reported hot Jupiters have orbital ...periods between 1.4 and 2.05 d. The masses of the three planets are 1.18 ± 0.14 MJ, 3.16 ± 0.12 MJ, and 2.30 ± 0.28 MJ, for TOI-1181b, TOI-1516b, and TOI-2046b, respectively. The stellar host of TOI-1181b is a F9IV star, whereas TOI-1516b and TOI-2046b orbit F main sequence host stars. The ages of the first two systems are in the range of 2–5 Gyrs. However, TOI-2046 is among the few youngest known planetary systems hosting a hot Jupiter, with an age estimate of 100–400 Myrs. The main instruments used for the radial velocity follow-up of these three planets are located at Ondřejov, Tautenburg, and McDonald Observatory, and all three are mounted on 2–3 m aperture telescopes, demonstrating that mid-aperture telescope networks can play a substantial role in the follow-up of gas giants discovered by TESS and in the future by PLATO.
Abell 70 (PN G038.1−25.4, hereafter A 70) is a planetary nebula known for its diamond ring appearance due to a superposition with a background galaxy. The previously unstudied central star is found ...to be a binary consisting of a G8IV-V secondary at optical wavelengths and a hot white dwarf at ultraviolet wavelengths. The secondary shows Ba ii and Sr ii features enhanced for its spectral type that, combined with the chromospheric Hα emission and possible 20-30 km s−1 radial velocity amplitude, firmly classifies the binary as a Barium star. The proposed origin of Barium stars is intimately linked to planetary nebulae (PNe) whereby wind accretion pollutes the companion with dredged-up material rich in carbon and s-process elements when the primary is experiencing thermal pulses on the asymptotic giant branch (AGB). A 70 provides further evidence for this scenario together with the other very few examples of Barium central stars. The nebula is found to have Type I chemical abundances with helium and nitrogen enrichment, which when combined with future abundance studies of the central star, will establish A 70 as a unique laboratory for studying s-process AGB nucleosynthesis. We also discuss guidelines to discover more binary central stars with cool secondaries in large orbits that are needed to balance our knowledge of binarity in PNe against the currently better studied post-common-envelope binary central stars.
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