Context. Protoplanetary disks show large diversity regarding their morphology and dust composition. With mid-infrared interferometry the thermal emission of disks can be spatially resolved, and the ...distribution and properties of the dust within can be studied. Aims. Our aim is to perform a statistical analysis on a large sample of 82 disks around low- and intermediate-mass young stars, based on mid-infrared interferometric observations. We intend to study the distribution of disk sizes, variability, and the silicate dust mineralogy. Methods. Archival mid-infrared interferometric data from the MIDI instrument on the Very Large Telescope Interferometer are homogeneously reduced and calibrated. Geometric disk models are used to fit the observations to get spatial information about the disks. An automatic spectral decomposition pipeline is applied to analyze the shape of the silicate feature. Results. We present the resulting data products in the form of an atlas, containing N band correlated and total spectra, visibilities, and differential phases. The majority of our data can be well fitted with a continuous disk model, except for a few objects, where a gapped model gives a better match. From the mid-infrared size–luminosity relation we find that disks around T Tauri stars are generally colder and more extended with respect to the stellar luminosity than disks around Herbig Ae stars. We find that in the innermost part of the disks (r ≲ 1 au) the silicate feature is generally weaker than in the outer parts, suggesting that in the inner parts the dust is substantially more processed. We analyze stellar multiplicity and find that in two systems (AB Aur and HD 72106) data suggest a new companion or asymmetric inner disk structure. We make predictions for the observability of our objects with the upcoming Multi-AperTure mid-Infrared SpectroScopic Experiment (MATISSE) instrument, supporting the practical preparations of future MATISSE observations of T Tauri stars.
Exocomets: A spectroscopic survey Rebollido, I.; Eiroa, C.; Montesinos, B. ...
Astronomy and astrophysics (Berlin),
07/2020, Letnik:
639
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
While exoplanets are now routinely detected, the detection of small bodies in extrasolar systems remains challenging. Since the discovery of sporadic events, which are interpreted to be ...exocomets (falling evaporating bodies) around
β
Pic in the early 1980s, only ∼20 stars have been reported to host exocomet-like events.
Aims.
We aim to expand the sample of known exocomet-host stars, as well as to monitor the hot-gas environment around stars with previously known exocometary activity.
Methods.
We have obtained high-resolution optical spectra of a heterogeneous sample of 117 main-sequence stars in the spectral type range from B8 to G8. The data were collected in 14 observing campaigns over the course of two years from both hemispheres. We analysed the Ca
II
K&H and Na
I
D lines in order to search for non-photospheric absorptions that originated in the circumstellar environment and for variable events that could be caused by the outgassing of exocomet-like bodies.
Results.
We detected non-photospheric absorptions towards 50% of the sample, thus attributing a circumstellar origin to half of the detections (i.e. 26% of the sample). Hot circumstellar gas was detected in the metallic lines inspected via narrow stable absorptions and/or variable blue- and red-shifted absorption events. Such variable events were found in 18 stars in the Ca
II
and/or Na
I
lines; six of them are reported in the context of this work for the first time. In some cases, the variations we report in the Ca
II
K line are similar to those observed in
β
Pic. While we do not find a significant trend in the age or location of the stars, we do find that the probability of finding CS gas in stars with larger
v
sin
i
is higher. We also find a weak trend with the presence of near-infrared excess and with anomalous (
λ
Boo-like) abundances, but this would require confirmation by expanding the sample.
Abstract
One possible explanation of the cavity in debris discs is the gravitational perturbation of an embedded giant planet. Planetesimals passing close to a massive body are dynamically stirred ...resulting in a cleared region known as the chaotic zone. Theory of overlapping mean-motion resonances predicts the width of this cavity. To test whether this cavity is identical to the chaotic zone, we investigate the formation of cavities by means of collisionless N-body simulations assuming a 1.25–10 Jupiter mass planet with eccentricities of 0–0.9. Synthetic images at millimetre wavelengths are calculated to determine the cavity properties by fitting an ellipse to 14 per cent contour level. Depending on the planetary eccentricity, epl, the elliptic cavity wall rotates as the planet orbits with the same (epl < 0.2) or half (epl > 0.2) period that of the planet. The cavity centre is offset from the star along the semimajor axis of the planet with a distance of $d=0.1q^{-0.17}e_\mathrm{pl}^{0.5}$ in units of cavity size towards the planet's orbital apocentre, where q is the planet-to-star mass ratio. Pericentre (apocentre) glow develops for epl < 0.05 (epl > 0.1), while both are present for 0.05 ≤ epl ≤ 0.1. Empirical formulae are derived for the sizes of the cavities: δacav = 2.35q0.36 and $\delta a_\mathrm{cav}=7.87q^{0.37}e_\mathrm{pl}^{0.38}$ for epl ≤ 0.05 and epl > 0.05, respectively. The cavity eccentricity, ecav, equals to that of the planet only for 0.3 ≤ epl ≤ 0.6. A new method based on Atacama Large Millimeter/submillimeter Array observations for estimating the orbital parameters and mass of the planet carving the cavity is also given.
The Solar System originated in a cloud of interstellar gas and dust. The dust is in the form of amorphous silicate particles and carbonaceous dust. The composition of cometary material, however, ...shows that a significant fraction of the amorphous silicate dust was transformed into crystalline form during the early evolution of the protosolar nebula. How and when this transformation happened has been a question of debate, with the main options being heating by the young Sun and shock heating. Here we report mid-infrared features in the outburst spectrum of the young Sun-like star EX Lupi that were not present in quiescence. We attribute them to crystalline forsterite. We conclude that the crystals were produced through thermal annealing in the surface layer of the inner disk by heat from the outburst, a process that has hitherto not been considered. The observed lack of cold crystals excludes shock heating at larger radii.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A significant fraction of main-sequence stars are encircled by dusty debris discs, where the short-lived dust particles are replenished through collisions between planetesimals. Most destructive ...collisions occur when the orbits of smaller bodies are dynamically stirred up, either by the gravitational effect of locally formed Pluto-sized planetesimals (self-stirring scenario), or via secular perturbation caused by an inner giant planet (planetary stirring). The relative importance of these scenarios in debris systems is unknown. Here, we present new Herschel Space Observatory imagery of 11 discs selected from the most massive and extended known debris systems. All discs were found to be extended at far-infrared wavelengths, five of them being resolved for the first time. We evaluated the feasibility of the self-stirring scenario by comparing the measured disc sizes with the predictions of the model calculated for the ages of our targets. We concluded that the self-stirring explanation works for seven discs. However, in four cases, the predicted pace of outward propagation of the stirring front, assuming reasonable initial disc masses, was far too low to explain the radial extent of the cold dust. Therefore, for HD 9672, HD 16743, HD 21997, and HD 95086, another explanation is needed. We performed a similar analysis for β Pic and HR 8799, reaching the same conclusion. We argue that planetary stirring is a promising possibility to explain the disc properties in these systems. In HR 8799 and HD 95086, we may already know the potential perturber, since their known outer giant planets could be responsible for the stirring process. Interestingly, the discs around HD 9672, HD 21997, and β Pic are also unique in harbouring detectable amount of molecular CO gas. Our study demonstrates that among the largest and most massive debris discs self-stirring may not be the only active scenario, and potentially planetary stirring is responsible for destructive collisions and debris dust production in a number of systems.
FU Orionis-type objects (FUors) are young stellar objects experiencing large optical outbursts due to highly enhanced accretion from the circumstellar disk onto the star. FUors are often surrounded ...by massive envelopes, which play a significant role in the outburst mechanism. Conversely, the subsequent eruptions might gradually clear up the obscuring envelope material and drive the protostar on its way to become a disk-only T Tauri star. Here we present an APEX 12CO and 13CO survey of eight southern and equatorial FUors. We measure the mass of the gaseous material surrounding our targets, locate the source of the CO emission, and derive physical parameters for the envelopes and outflows, where detected. Our results support the evolutionary scenario where FUors represent a transition phase from envelope-surrounded protostars to classical T Tauri stars.
ABSTRACT The overtone and multi-mode RR Lyrae stars in the globular cluster M3 are studied using a 200 day long, , and time-series photometry obtained in 2012. 70% of the 52 overtone variables ...observed show some kind of multi-periodicity (with additional frequency at frequency ratio, Blazhko effect, double/multi-mode pulsation, and period doubling). A signal at the 0.587 frequency ratio to the fundamental-mode frequency is detected in the double-mode star, V13, which may be identified as the second radial overtone mode. If this mode identification is correct, than V13 is the first RR Lyrae star showing triple-mode pulsation of the first three radial modes. Either the Blazhko effect or the frequency (or both of these phenomena) appears in seven double-mode stars. The period ratio of RRd stars showing the Blazhko effect are anomalous. A displacement of the main frequency component at the fundamental mode with the value of modulation frequency (or its half), is detected in three Blazhko RRd stars that are parallel with the appearance of the overtone-mode pulsation. The frequency appears in RRc stars that lie at the blue side of the double-mode region and in RRd stars, raising the suspicion that its occurrence may be connected to double-mode pulsation. The changes of the Blazhko and double-mode properties of the stars are also reviewed using the recent and archive photometric data.
The young star population of Lynds 1188 Szegedi-Elek, E; Kun, M; Moór, A ...
Monthly notices of the Royal Astronomical Society,
04/2019, Letnik:
484, Številka:
2
Journal Article
Context. HBC 722 (V2493 Cyg) is a young eruptive star in outburst since 2010. Spectroscopic evidence suggests that the source is an FU Orionis-type object, with an atypically low outburst luminosity. ...Aims. Because it was well characterized in the pre-outburst phase, HBC 722 is one of the few FUors from which we can learn about the physical changes and processes associated with the eruption, including the role of the circumstellar environment. Methods. We monitored the source in the BVRIJHKS bands from the ground and at 3.6 and 4.5 μm from space with the Spitzer Space Telescope. We analyzed the light curves and studied the evolving spectral energy distribution by fitting a series of steady accretion disk models at many epochs covering the outburst. We also analyzed the spectral properties of the source based on our new optical and infrared spectra, comparing our line inventory with those published in the literature for other epochs. We also mapped HBC 722 and its surroundings at millimeter wavelengths. Results. From the light-curve analysis we conclude that the first peak of the outburst in 2010 September was mainly due to an abrupt increase in the accretion rate in the innermost part of the system. This was followed after a few months by a long-term process, when the brightening of the source was mainly due to a gradual increase in the accretion rate and the emitting area. Our new observations show that the source is currently in a constant plateau phase. We found that the optical spectrum was similar in the first peak and following periods, but around the peak the continuum was bluer and the Hα profile changed significantly between 2012 and 2013. The source was not detected in the millimeter continuum, but we discovered a flattened molecular gas structure with a diameter of 1700 au and mass of 0.3 M⊙ centered on HBC 722. Conclusions. While the first brightness peak might be interpreted as a rapid fall of piled-up material from the inner disk onto the star, the later monotonic flux rise suggests the outward expansion of a hot component according to a previously described theory. Our study of HBC 722 demonstrates that accretion-related outbursts can occur in young stellar objects even with very low-mass disks in the late Class II phase.
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