Matthias R. Schreiber

VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way

Original article can be found at: http://www.sciencedirect.com/science/journal/13841076 Copyright Elsevier B.V.

Flows of gas through a protoplanetary gap.

The formation of gaseous giant planets is thought to occur in the first few million years after stellar birth. Models predict that the process produces a deep gap in the dust component (shallower in the gas). Infrared observations of the disk around the young star HD 142527 (at a distance of about 140 parsecs from Earth) found an inner disk about 10 astronomical units (au) in radius (1 au is the Earth–Sun distance), surrounded by a particularly large gap and a disrupted outer disk beyond 140 au. This disruption is indicative of a perturbing planetary-mass body at about 90 au. Radio observations indicate that the bulk mass is molecular and lies in the outer disk, whose continuum emission has a horseshoe morphology. The high stellar accretion rate would deplete the inner disk in less than one year, and to sustain the observed accretion matter must therefore flow from the outer disk and cross the gap. In dynamical models, the putative protoplanets channel outer-disk material into gap-crossing bridges that feed stellar accretion through the inner disk. Here we report observations of diffuse CO gas inside the gap, with denser HCO+ gas along gap-crossing filaments. The estimated flow rate of the gas is in the range of 7 × 10−9 to 2 × 10−7 solar masses per year, which is sufficient to maintain accretion onto the star at the present rate.1. Departamento de Astronomı́a, Universidad de Chile, Casilla 36-D, Santiago, Chile 2. Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura 763-0355, Santiago Chile 3. European Southern Observatory (ESO), Casilla 19001, Vitacura, Santiago, Chile 4. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA 5. Observatoire de Genève, Université de Genève, 51 ch. des Maillettes, 1290, Versoix, Switzerland 6. Departamento de Astronomı́a y Astrofı́sica, Pontificia Universidad Católica de Chile, Santiago, Chile 7. UMI-FCA, CNRS / INSU France (UMI 3386) , and Departamento de Astronomı́a, Universidad de Chile, Santiago, Chile. 8. CNRS / UJF Grenoble 1, UMR 5274, Institut de Planétologie et dAstrophysique de Grenoble (IPAG), France 9. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 USA 10. Department of Astronomy, U. C. Berkeley, 601 Campbell Hall, Berkeley, CA 94720 11. Departamento de Fı́sica y Astronomı́a, Universidad Valparaiso, Av. Gran Bretana 111, Valparaiso, Chile. 12. University Observatory, Ludwig-Maximillians University, Munich.

Two planets orbiting the recently formed post-common envelope binary NN Serpentis

Planets orbiting post-common envelope binaries provide fundamental information on planet formation and evolution. We searched for such planets in NN Ser ab, an eclipsing short-period binary that shows long-term eclipse time variations. Using published, reanalysed, and new mid-eclipse times of NN Ser ab obtained between 1988 and 2010, we find excellent agreement with the light-travel-time effect produced by two additional bodies superposed on the linear ephemeris of the binary. Our multi-parameter fits accompanied by N-body simulations yield a best fit for the objects NN Ser (ab)c and d locked in the 2:1 mean motion resonance, with orbital periods P-c similar or equal to 15.5 yrs and P-d similar or equal to 7.7 yrs, masses M-c sin i(c) similar or equal to 6.9 M-Jup and M-d sin i(d) similar or equal to 2.2 M-Jup, and eccentricities e(c) similar or equal to 0 and e(d) similar or equal to 0.20. A secondary chi(2) minimum corresponds to an alternative solution with a period ratio of 5:2. We estimate that the progenitor binary consisted of an A star with similar or equal to 2 M-circle dot and the present M dwarf secondary at an orbital separation of similar to 1.5 AU. The survival of two planets through the common-envelope phase that created the present white dwarf requires fine tuning between the gravitational force and the drag force experienced by them in the expanding envelope. The alternative is a second-generation origin in a circumbinary disk created at the end of this phase. In that case, the planets would be extremely young with ages not exceeding the cooling age of the white dwarf of 10(6) yrs.

The Nature of Transition Circumstellar Disks. III. Perseus, Taurus, and Auriga

As part of an ongoing program aiming to characterize a large number of Spitzer-selected transition disks (disks with reduced levels of near-IR and/or mid-IR excess emission), we have obtained (sub)millimeter wavelength photometry, high-resolution optical spectroscopy, and adaptive optics near-infrared imaging for a sample of 31 transition objects located in the Perseus, Taurus, and Auriga molecular clouds. We use these ground-based data to estimate disk masses, multiplicity, and accretion rates in order to investigate the mechanisms potentially responsible for their inner holes. Following our previous studies in other regions, we combine disk masses, accretion rates, and multiplicity data with other information, such as spectral energy distribution morphology and fractional disk luminosity, to classify the disks as strong candidates for the following categories: grain-growth-dominated disks (seven objects), giant planet-forming disks (six objects), photoevaporating disks (seven objects), debris disks (11 objects), and cicumbinary disks (one object, which was also classified as a photoevaporating disk). Combining our sample of 31 transition disks with those from our previous studies results in a sample of 74 transition objects that have been selected, characterized, and classified in a homogenous way. We discuss this combined high-quality sample in the context of the current paradigm of the evolution and dissipation of protoplanetary disks and use its properties to constrain different aspects of the key processes driving their evolution. We find that the age distribution of disks that are likely to harbor recently formed giant planets favors core accretion as the main planet formation mechanism and a ∼2–3 Myr formation timescale.

Imaging the water snow-line during a protostellar outburst

A snow-line is the region of a protoplanetary disk at which a major volatile, such as water or carbon monoxide, reaches its condensation temperature. Snow-lines play a crucial role in disk evolution by promoting the rapid growth of ice-covered grains. Signatures of the carbon monoxide snow-line (at temperatures of around 20 kelvin) have recently been imaged in the disks surrounding the pre-main-sequence stars TW Hydra and HD163296 (refs 3, 10), at distances of about 30 astronomical units (au) from the star. But the water snow-line of a protoplanetary disk (at temperatures of more than 100 kelvin) has not hitherto been seen, as it generally lies very close to the star (less than 5 au away for solar-type stars). Water-ice is important because it regulates the efficiency of dust and planetesimal coagulation, and the formation of comets, ice giants and the cores of gas giants. Here we report images at 0.03-arcsec resolution (12 au) of the protoplanetary disk around V883 Ori, a protostar of 1.3 solar masses that is undergoing an outburst in luminosity arising from a temporary increase in the accretion rate. We find an intensity break corresponding to an abrupt change in the optical depth at about 42 au, where the elevated disk temperature approaches the condensation point of water, from which we conclude that the outburst has moved the water snow-line. The spectral behaviour across the snow-line confirms recent model predictions: dust fragmentation and the inhibition of grain growth at higher temperatures results in soaring grain number densities and optical depths. As most planetary systems are expected to experience outbursts caused by accretion during their formation, our results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation.

Cataclysmic variables from the Sloan Digital Sky Survey. VIII. The final year (2007–2008)

This paper completes the series of cataclysmic variables (CVs) identified from the Sloan Digital Sky Survey (SDSS) I/II. The coordinates, magnitudes, and spectra of 33 CVs are presented. Among the 33 are eight systems known prior to SDSS (CT Ser, DO Leo, HK Leo, IR Com, V849 Her, V405 Peg, PG1230+226, and HS0943+1404), as well as nine objects recently found through various photometric surveys. Among the systems identified since the SDSS are two polar candidates, two intermediate polar candidates, and one candidate for containing a pulsating white dwarf. Our follow-up data have confirmed a polar candidate from Paper VII and determined tentative periods for three of the newly identified CVs. A complete summary table of the 285 CVs with spectra from SDSS I/II is presented as well as a link to an online table of all known CVs from both photometry and spectroscopy that will continue to be updated as future data appear.

Cataclysmic variables from SDSS. VII. The seventh year (2006)

Coordinates, magnitudes, and spectra are presented for 39 cataclysmic variables (CVs) found in Sloan Digital Sky Survey (SDSS) spectra that were primarily obtained in 2006. Of these, 13 were CVs identified prior to the SDSS spectra (AK Cnc, GY Cnc, GO Com, ST LMi, NY Ser, MR Ser, QW Ser, EU UMa, IY UMa, HS1340+ 1524, RXJ1610.1+0352, Boo 1, Leo 5). Follow-up spectroscopic observations of seven systems (including one from year 2005 and another from year 2004) were obtained, resulting in estimates of the orbital periods for three objects. The new CVs include two candidates for high inclination, eclipsing systems, four new polars, and three systems whose spectra clearly reveal atmospheric absorption lines from the underlying white dwarf.

THE NATURE OF TRANSITION CIRCUMSTELLAR DISKS. II. SOUTHERN MOLECULAR CLOUDS

Transition disk objects are pre-main-sequence stars with little or no near-IR excess and significant far-IR excess, implying inner opacity holes in their disks. Here we present a multifrequency study of transition disk candidates located in Lupus I, III, IV, V, VI, Corona Australis, and Scorpius. Complementing the information provided by Spitzer with adaptive optics (AO) imaging (NaCo, VLT), submillimeter photometry (APEX), and echelle spectroscopy (Magellan, Du Pont Telescopes), we estimate the multiplicity, disk mass, and accretion rate for each object in our sample in order to identify the mechanism potentially responsible for its inner hole. We find that our transition disks show a rich diversity in their spectral energy distribution morphology, have disk masses ranging

Monte Carlo simulations of post-common-envelope white dwarf + main sequence binaries: comparison with the SDSS DR7 observed sample

Context. Detached white dwarf + main sequence (WD+MS) systems represent the simplest population of post-common envelope binaries (PCEBs). Since the ensemble properties of this population carries important information about the characteristics of the common-envelope (CE) phase, it deserves close scrutiny. However, most population synthesis studies do not fully consider the effects of the observational selection biases of the samples used to compare with the theoretical simulations. Aims. Here we present the results of a set of detailed Monte Carlo simulations of the population of WD+MS binaries in the Sloan Digital Sky Survey (SDSS) Data Release 7. Methods. We used up-to-date stellar evolutionary models, a complete treatment of the Roche lobe overflow episode, and a full implementation of the orbital evolution of the binary systems. Moreover, in our treatment we took the selection criteria and all the known observational biases into account. Results. Our population synthesis study allowed us to make a meaningful comparison with the available observational data. In particular, we examined the CE efficiency, the possible contribution of internal energy, and the initial mass ratio distribution (IMRD) of the binary systems. We find that our simulations correctly reproduce the properties of the observed distribution of WD+MS PCEBs. In particular, we find that once the observational biases are carefully considered, the distribution of orbital periods and of masses of the WD and MS stars can be correctly reproduced for several choices of the free parameters and different IMRDs, although models in which a moderate fraction (≤10%) of the internal energy is used to eject the CE and in which a low value of CE efficiency is used (≤0.3) seem to fit the observational data better. We also find that systems with He-core WDs are over-represented in the observed sample, because of selection effects. Conclusions. Although our study represents an important step forward in modeling the population of WD+MS PCEBs, the still scarce observational data preclude deriving a precise value of the several free parameters used to compute the CE phase without ambiguity or ascertaining which the correct IMRD might be.

Submillimeter Array Observations of the RX J1633.9-2442 Transition Disk: Evidence for Multiple Planets in the Making

We present continuum high-resolution Submillimeter Array (SMA) observations of the transition disk object RX?J1633.9-2442, which is located in the Ophiuchus molecular cloud and has recently been identified as a likely site of ongoing giant planet formation. The observations were taken at 340 GHz (880 ?m) with the SMA in its most extended configuration, resulting in an angular resolution of 03 (35?AU at the distance of the target). We find that the disk is highly inclined (i ~ 50?) and has an inner cavity ~25?AU in radius, which is clearly resolved by our observations. We simultaneously model the entire optical to millimeter wavelength spectral energy distribution and SMA visibilities of RX?J1633.9-2442 in order to constrain the structure of its disk. We find that an empty cavity ~25?AU in radius is inconsistent with the excess emission observed at 12, 22, and 24 ?m. Instead, the mid-IR excess can be modeled by either a narrow, optically thick ring at ~10?AU or an optically thin region extending from ~7?AU to ~25?AU. The inner disk (r 5?AU) is mostly depleted of small dust grains as attested by the lack of detectable near-IR excess. We also present deep Keck aperture masking observations in the near-IR, which rule out the presence of a companion up to 500 times fainter than the primary star (in K band) for projected separations in the 5-20?AU range. We argue that the complex structure of the RX?J1633.9-2442 disk is best explained by multiple planets embedded within the disk. We also suggest that the properties and incidence of objects such as RX?J1633.9-2442, T?Cha, and LkCa?15 (and those of the companions recently identified to these two latter objects) are most consistent with the runaway gas accretion phase of the core accretion model, when giant planets gain their envelopes and suddenly become massive enough to open wide gaps in the disk.