X-Shooter observations of low-mass stars in the Eta Chamaeleontis association

The nearby Eta Chamaeleontis association is a collection of 4-10 Myr old stars with a disk fraction of 35-45%. In this study, the broad wavelength coverage of VLT/X-Shooter is used to measure the stellar and mass accretion properties of 15 low mass stars in the Eta Chamaeleontis association. For each star, the observed spectrum is fitted with a non-accreting stellar template and an accretion spectrum obtained from assuming a plane-parallel hydrogen slab. Five of the eight stars with an IR disk excess show excess UV emission, indicating ongoing accretion. The accretion rates measured here are similar to those obtained from previous measurements of excess UV emission, but tend to be higher than past measurements from H-alpha modeling. The mass accretion rates are consistent with those of other young star forming regions.Comment: Accepted for publication in Astronomy & Astrophysic

What have they been up to in Lübeck recently

This talk will give an overview over three related research prototypes for ambient interactive systems. We start by introducing NEMO, the Network Environment for Multimedia Objects. NEMO is a smart media environment for semantically rich, personalised, and device-specific access to and interaction with multimedia objects. Next, a shared electronic whiteboard called ShareBoard is decribed. The goal of ShareBoard is to deliver a natural user interface to working with electronic whiteboards. Integrated within ShareBoard are input devices to recognise the movement of users in the surrounding space and for sensing 3D-gesture. ShareBoard can make use of media objects in NEMO. Last, we introduce the Modular Awareness Construction Kit. MACK is a framework for developing context aware, ambient intelligent systems that blend seamlessly with the users’ everyday route, enabling unobtrusive in-situ interaction and facilitating enhanced cooperation and communication. In the future, MACK is to deliver contextual information to both NEMO and ShareBoard

Double Kerr-Schild spacetimes and the Newman-Penrose map

The Newman-Penrose map, which is closely related to the classical double copy, associates certain exact solutions of Einstein's equations with self-dual solutions of the vacuum Maxwell equations. Here we initiate an extension of the Newman-Penrose map to a broader class of spacetimes. As an example, we apply principles from the Newman-Penrose map to associate a self-dual gauge field to the Kerr-Taub-NUT-(A)dS spacetime and we show that the result agrees with previously studied examples of classical double copies. The corresponding field strength exhibits a discrete electric-magnetic duality that is distinct from its (Hodge star) self-dual property.Comment: 14 pages + reference

An ALMA Constraint on the GSC 6214-210 B Circum-Substellar Accretion Disk Mass

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of GSC 6214-210 A and B, a solar-mass member of the 5-10 Myr Upper Scorpius association with a 15 $\pm$ 2 Mjup companion orbiting at $\approx$330 AU (2.2"). Previous photometry and spectroscopy spanning 0.3-5 $\mu$m revealed optical and thermal excess as well as strong H$\alpha$ and Pa~$\beta$ emission originating from a circum-substellar accretion disk around GSC 6214-210 B, making it the lowest mass companion with unambiguous evidence of a subdisk. Despite ALMA's unprecedented sensitivity and angular resolution, neither component was detected in our 880 $\mu$m (341 GHz) continuum observations down to a 3-$\sigma$ limit of 0.22 mJy/beam. The corresponding constraints on the dust mass and total mass are <0.15 Mearth and <0.05 Mjup, respectively, or <0.003% and <0.3% of the mass of GSC 6214-210 B itself assuming a 100:1 gas-to-dust ratio and characteristic dust temperature of 10-20 K. If the host star possesses a putative circum-stellar disk then at most it is a meager 0.0015% of the primary mass, implying that giant planet formation has certainly ceased in this system. Considering these limits and its current accretion rate, GSC 6214-210 B appears to be at the end stages of assembly and is not expected to gain any appreciable mass over the next few Myr.Comment: Accepted to ApJ

Star formation in W3 - AFGL333: Young stellar content, properties and roles of external feedback

One of the key questions in the field of star formation is the role of stellar feedback on subsequent star formation process. The W3 giant molecular cloud complex at the western border of the W4 super bubble is thought to be influenced by the stellar winds of the massive stars in W4. AFGL333 is a ~10^4 Msun cloud within W3. This paper presents a study of the star formation activity within AFGL333 using deep JHKs photometry obtained from the NOAO Extremely Wide-Field Infrared Imager combined with Spitzer-IRAC-MIPS photometry. Based on the infrared excess, we identify 812 candidate young stellar objects in the complex, of which 99 are classified as Class I and 713 are classified as Class II sources. The stellar density analysis of young stellar objects reveals three major stellar aggregates within AFGL333, named here AFGL333-main, AFGL333-NW1 and AFGL333-NW2. The disk fraction within AFGL333 is estimated to be ~50-60%. We use the extinction map made from the H-Ks colors of the background stars to understand the cloud structure and to estimate the cloud mass. The CO-derived extinction map corroborates the cloud structure and mass estimates from NIR color method. From the stellar mass and cloud mass associated with AFGL333, we infer that the region is currently forming stars with an efficiency of ~4.5% and at a rate of ~2 - 3 Msun Myr-1pc-2. In general, the star formation activity within AFGL333 is comparable to that of nearby low mass star-forming regions. We do not find any strong evidence to suggest that the stellar feedback from the massive stars of nearby W4 super bubble has affected the global star formation properties of the AFGL333 region.Comment: 17 pages, 9 figures, Accepted for publication in Ap

The Ages of Optically Bright Sub-Clusters in the Serpens Star-Forming Region

The Serpens Molecular Cloud is one of the most active star-forming regions within 500 pc, with over one thousand of YSOs at different evolutionary stages. The ages of the member stars inform us about the star formation history of the cloud. In this paper, we develop a spectral energy distribution (SED) fitting method for nearby evolved (diskless) young stars from members of the Pleiades to estimate their ages, with a temperature scale adopted from APOGEE spectra. When compared with literature temperatures of selected YSOs in Orion, the SED fits to cool (<5000 K) stars have temperatures that differ by an average of <~ 50 K and have a scatter of ~ 210 K for both disk-hosting and diskless stars. We then apply this method to YSOs in the Serpens Molecular Cloud to estimate ages of optical members previously identified from Gaia DR2 astrometry data. The optical members in Serpens are concentrated in different subgroups with ages from ~4 Myr to ~22 Myr; the youngest clusters, W40 and Serpens South, are dusty regions that lack enough optical members to be included in this analysis. These ages establish that the Serpens Molecular Cloud has been forming stars for much longer than has been inferred from infrared surveys.Comment: 28 pages, 22 figures, accepted for publication in The Astrophysical Journa

Herschel/PACS View Of Disks Around Low-Mass Stars And Brown Dwarfs In The TW Hydrae Association

We conducted Herschel/PACS observations of five very low-mass stars or brown dwarfs located in the TW Hya association with the goal of characterizing the properties of disks in the low stellar mass regime. We detected all five targets at 70 mu m and 100 mu m and three targets at 160 mu m. Our observations, combined with previous photometry from 2MASS, WISE, and SCUBA-2, enabled us to construct spectral energy distributions (SEDs) with extended wavelength coverage. Using sophisticated radiative transfer models, we analyzed the observed SEDs of the five detected objects with a hybrid fitting strategy that combines the model grids and the simulated annealing algorithm and evaluated the constraints on the disk properties via the Bayesian inference method. The modeling suggests that disks around low-mass stars and brown dwarfs are generally flatter than their higher mass counterparts, but the range of disk mass extends to well below the value found in T Tauri stars, and the disk scale heights are comparable in both groups. The inferred disk properties (i.e., disk mass, flaring, and scale height) in the low stellar mass regime are consistent with previous findings from large samples of brown dwarfs and very low-mass stars. We discuss the dependence of disk properties on their host stellar parameters and find a significant correlation between the Herschel far-IR fluxes and the stellar effective temperatures, probably indicating that the scaling between the stellar and disk masses (i.e., M-disk proportional to M-star) observed mainly in low-mass stars may extend down to the brown dwarf regime.Natural Science Foundation of Jiangsu Province of China BK20141046Youth Qianren Program of the National Science Foundation of ChinaNational Aeronautics and Space AdministrationStrategic Priority Research Program >The Emergence of Cosmological Structures> of the Chinese Academy of Sciences XDB09000000Astronom