Search

Context. Circumstellar disks are expected to be planet birthplaces. The potential for forming one or more planets of various masses is essentially driven by the initial mass of the disks, a crucial parameter for any planet formation theory. Constraining the masses of disks is of great interest for low-mass stars, which are expected to harbor less massive disks. Aims. We present and analyze Herschel/PACS observations of disk-bearing M-type stars that belong to the young ∼2 Myr old Chamaleon-I star-forming region, to better constrain the properties of the circumstellar material and the stellar mass dependence of these parameters. Methods. We used the radiative transfer code RADMC to successfully model the spectral energy distributions (SEDs) of 17 M-type stars detected at PACS wavelengths. Our modeling strategy is carefully designed so that we search for the most probable disks parameters among a large grid of models, via Bayesian inference, which is an approach that has already proven successful. Results. Based on the modeling results, we first discuss the relatively low detection rates of M5 and later spectral type stars with respect to the PACS sensitivity, and argue that their disks masses, or flaring indices, are likely to be low (Mdisk ∼ 10-5 M, ∼ 1:1). For M0 to M3 stars, we find a relatively broad range of disk masses (10-4-10-3 M☉), scale heights, and flaring indices. Via a parametrization of dust stratification, we can reproduce the peak fluxes of the 10 μm emission feature observed with Spitzer/IRS, and find that disks around M-type stars may display signs of dust sedimentation. We discuss a tentative correlation between the strength of the 10 μm emission feature and the parametrized stratification. Conclusions. The Herschel/PACS observations of low-mass stars in Cha-I provide new constraints on their disk properties, overall suggesting that disk parameters for early M-type stars are comparable to those for more massive stars (e.g., comparable scale height and flaring angles). However, regions of the disks emitting at about 100 μm may still be in the optically thick regime, preventing direct determination of disk masses. Thus the modeled disk masses should be considered as lower limits. Nevertheless, we are able to extend the wavelength coverage of SED models and start characterizing effects, such as dust sedimentation, an effort leading the way towards ALMA observations of these low-mass stars. [ABSTRACT FROM AUTHOR]

We discover that the very low-mass brown dwarf OTS 44 (M9.5, ~12 MJup) has significant accretion and a substantial disk, which demonstrates that the processes that accompany canonical star formation occur down to a central mass of a few Jupiter masses. We discover in VLT/SINFONI spectra that OTS 44 has strong, broad, and variable Pa β emission that is evidence for active accretion at the planetary border. We also detect strong Hα emission of OTS 44 in a literature spectrum and determine an Hα EW of -141Å, which indicates active accretion. Both the Pa β and Hα emission lines have broad profiles with wings extending to velocities of about ±200 km s-1. We determine the mass accretion rate of OTS 44 based on Hα to 7.6 × 10-12 M☉ yr-1. This result shows that OTS 44 has a relatively high mass-accretion rate considering its small central mass. This mass rate is nevertheless consistent with the general decreasing trend found for stars of several solar masses down to brown dwarfs. Furthermore, we determine the properties of the disk surrounding OTS 44 through radiative transfer modeling of flux measurement from the optical to the far-IR (Herschel) by applying a Bayesian analysis. We find that OTS 44 has a highly flared disk (β > 1.2) with a mass of 9.1 +1.7 -5.5 ×10-5 M☉, i.e. ~0.1 MJup or 30 MEarth. We show that the ratio of the disk-to-central-mass of about 10-2 found for objects between 0.03 M☉ and 14 M☉ is also valid for OTS 44 at a mass of ~0.01 M☉. Our observations are in line with an isolated star-like mode of the formation of brown dwarfs down to 0.01 M☉. [ABSTRACT FROM AUTHOR]

Characterization of the properties of young brown dwarfs are important to constraining the formation of objects at the extreme low-mass end of the initial mass function. While young brown dwarfs share many properties with solar-mass T Tauri stars, differences may be used as tests of how the physics of accretion/outflow and disk chemistry/dissipation depend on the mass of the central object. This article summarizes the presentations and discussions during the splinter session on 'Disks, accretion and outflows of brown dwarfs' held at the CoolStars17 conference in Barcelona in June 2012. Recent results in the field of brown dwarf disks and outflows include the determination of brown dwarf disk masses and geometries based on Herschel far-IR photometry (70-160 µm), accretion properties based on X-Shooter spectra, and new outflow detections in the very low-mass regime. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Kinematic investigations are being increasingly deployed in studies of the lowest mass stars and brown dwarfs to investigate their origins, characterize their atmospheres, and examine the evolution of their physical parameters. This article summarizes the contributions made at the 'Kinematics of Very Low Mass Dwarfs' splinter session. Results discussed include analysis of kinematic distributions of M, L, and T dwarfs; theoretical tools for interpreting these distributions; identifications of very low mass halo dwarfs and wide companions to nearby stars; radial velocity variability among young and very cool brown dwarfs; and the search and identification of M dwarfs in young moving groups. A summary of discussion points at the conclusion of the splinter sesseion is also presented. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We show that the very young brown dwarf candidate ISO 217 (M6.25) is driving an intrinsically asymmetric bipolar outflow with a stronger and slightly faster red-shifted component based on spectro-astrometry of forbidden [S II] emission lines at 6716 Å and 6731 Å observed in UVES/VLT spectra taken in 2009. ISO 217 is only one of a handful of brown dwarfs and very low-mass stars (M5-M8) for which an outflow has been detected and that show that the T Tauri phase continues at the substellar limit. We measure a spatial extension of the outflow in [S II] of up to ± 190 mas (about ± 30 AU) and velocities of up to ± 40-50 km s-1. We find that the basic outflow properties (spatial extension, velocities, and outflow position angle) are of similar order as those determined in the discovery spectra from May 2007 of Whelan and coworkers. We show that the velocity asymmetry between both lobes is variable on timescales of a few years and that the strong asymmetry of a factor of two found in 2007 might be smaller than originally anticipated when using a more realistic stellar rest-velocity. We also detect forbidden line emission of [Fe II]λ7155 Å, for which we propose as a potential origin the hot inner regions of the outflow. To comprehensively understand the ISO 217 system, we determine the properties of its accretion disk based on radiative transfer modeling of the SED from 0.66 to 24 μm. This disk model agrees very well with Herschel/PACS data at 70 μm. We find that the disk is flared and intermediately inclined (i ~ 45°). The total disk mass of the best-fit model is 4 × 10-6 M⊙, which is low compared to the accretion and outflow rate of ISO 217 from the literature (~10-10 M⊙ yr-1). We propose that this discrepancy can be explained by either a higher disk mass than inferred from the model because of strong undetected grain growth and/or by an on average lower accretion rate and outflow rate than the determined values. We show that a disk inclination significantly exceeding 45°, as suggested from Hα modeling and from both lobes of the outflow being visible, is inconsistent with the SED data. Thus, despite its intermediate inclination angle, the disk of this brown dwarf does not appear to obscure the red outflow component in [S II], which is very rarely seen for T Tauri objects (only one other case). [ABSTRACT FROM AUTHOR]

The pre-main sequence star CHXR74 (M4.25) in Chamaeleon I was found a few years ago to be a very low-mass spectroscopic binary. A determination of its mass would provide a valuable dynamical mass measurement at young ages in the poorly constrained mass regime of <0.3 M☉.We carried out follow-up radial velocity monitoring with UVES/VLT between 2008 and 2011 and high-resolution adaptive-optic-assisted imaging with NACO/VLT in 2008 with the aim of constraining the binary orbit.We present an orbital solution of the system based on the combined radial velocity data set, which spans more than eleven years of UVES monitoring for CHXR74. The best-fit Kepler model has an orbital period of 13.1 years, zero eccentricity, and a radial velocity semi-amplitude of 2.2 kms-1. A companion mass M2 sin i (which is a lower limit due to the unknown orbital inclination i) of 0.08 M☉ is derived by using a modeldependent mass estimate for the primary of 0.24 Mv. The binary separation (a1 sin i + a2) for an inclination of 90° is 3.8AU, which corresponds to 23 mas. Complementary NACO/VLT images of CHXR74 were taken with the aim to directly resolve the binary. While there are marginal signs of an extended point spread function (PSF), we have detected no convincing companion to CHXR74 in the NACO images. From the non-detection of the companion together with a prediction of the binary separation at the time of the NACO observations, we derive an upper limit for the K-band brightness ratio of the two binary components of 0.5. This allows us to estimate an upper limit of the companion mass of 0.14 M☉ by applying evolutionary models. Thus, we confirm that CHXR74 is a very low-mass spectroscopic binary and constrain the secondary mass to lie within the range of about 0.08 and 0.14 M☉. We predict an astrometric signal of the primary between 0.2 and 0.4mas when taking into account the luminosity of the companion. The Gaia astrometric mission might well be able to solve the astrometric orbit of the primary and in combination with the presented radial velocity data determine an absolute companion mass. [ABSTRACT FROM AUTHOR]

One of the handful of known PMS eclipsing binaries is a component of the spectroscopic triple TY CrA. Its secondary component is particularly interesting since it is a star of relatively high mass (1.64 M⊙) which is still on the pre-main sequence. The eclipsing binary was analyzed in the optical wavelength range ~10 years ago, however, the crucial secondary eclipse minimum is very shallow. Therefore, we are obtaining new photometry in both optical and near-IR bands. We present first observations in (BVRI) which show that the secondary eclipse depth increases to about 0.1 mag in the I band. The increased eclipse depth with respect to other bands will help to better determine the colours and dimensions of the system. Furthermore, we show and discuss first near-IR observations of the primary eclipse. In addition to the light curves we are obtaining radial velocities in order to pin down the orbital parameters of the triple. Our first observations agree with the orbital parameters derived ~10 years ago. [ABSTRACT FROM PUBLISHER]

Astrometric observations of binary brown dwarfs yield dynamical masses of the components independently of theoretical models. We give an update on our long-term high-resolution spectroscopic and photometric monitoring programme of spatially resolved binary brown dwarfs using ground-based adaptive optics and the Hubble Space Telescope. We present current orbital fits, including refined dynamical mass estimate of the Kelu-1 AB system. The results seem to support the previously reported trend that evolutionary and atmospheric models might underestimate the mass of very-low-mass stars and brown dwarfs. [ABSTRACT FROM PUBLISHER]

The aim of the study was to evaluate the practicability and efficacy of a structured treatment and teaching programme (STTP) for type 2 diabetic outpatients on conventional insulin treatment after introducing remuneration for physicians. Reimbursement policy for the STTP was introduced in the state of Brandenburg, Germany, in July 1993. Between August 1993 and February 1994, 108 physicians and their assistants participated in a postgraduate seminar, which is a prerequisite for remuneration. A standardised interview was performed with 103 physicians and their paramedical personnel. Twenty of the practices who had performed STTP were visited in order to collect data on all the patients who had participated in the programme up to September, 1994. Within the first year already 10% of the target group of physicians participated in the seminars. The seminar and the programme were very well accepted. An improvement of HbA1c levels was observed in patients who had started insulin treatment (n = 35: 9.7 +/- 1.6% of total Hb before, 8.2 +/- 1.3% of total Hb after the programme) and in those who were already being treated with insulin before the STTP (n = 125: 9.6 +/- 2.5% of total Hb before, 8.1 +/- 1.4% of total Hb after the programme). The results of the study demonstrate the efficacy and practicability of an STTP for type 2 diabetic patients on conventional insulin therapy in ambulatory health care.

Beginning in July 1991, office-based physicians in Germany were remunerated for providing a structured treatment and teaching program to non-insulin-treated type II diabetic patients. The treatment and teaching program is based upon the respective recommendations of the German Diabetes Association. This article describes the structure of the program and the courses for general practitioners and their nurses. The prospective studies proving the beneficial effects of the program are summarized.