Solar-mass stars form via disk-mediated accretion. Recent findings indicate that this process is probably episodic in the form of accretion bursts 1 , possibly caused by disk fragmentation 2-4 . Although it cannot be ruled out that high-mass young stellar objects arise from the coalescence of their low-mass brethren 5 , the latest results suggest that they more likely form via disks 6-9 . It follows that disk-mediated accretion bursts should occur 10,11 . Here we report on the discovery of the first disk-mediated accretion burst from a roughly twenty-solar-mass high-mass young stellar object 12 . Our near-infrared images show the brightening of the central source and its outflow cavities. Near-infrared spectroscopy reveals emission lines typical for accretion bursts in low-mass protostars, but orders of magnitude more luminous. Moreover, the released energy and the inferred mass-accretion rate are also orders of magnitude larger. Our results identify disk-accretion as the common mechanism of star formation across the entire stellar mass spectrum.S255IR NIRS 3 (aka S255IR-SMA1) is a well-studied ∼20 M (L bol ∼ 2.4×10 4 L ) high-mass young stellar object (HMYSO) 13,14 in the S255IR massive star-forming region 13 , located at a distance of ∼1.8 kpc 15 . It exhibits a disk-like rotating structure 13 , very likely an accretion disk, viewed nearly edge-on 16 (inclination angle ∼80 • ).A molecular outflow has been detected 13 (blueshifted lobe position angle (P.A.) ∼247 • ) perpendicular to the disk. Two bipolar lobes (cavities), cleared by the outflow, are illuminated by the central source and show up as reflection nebulae towards the southwest (blueshifted lobe) and northeast (redshifted lobe, see Fig.

We report results from the first deep millimeter continuum survey targeting Brown Dwarfs (BDs). The survey led to the first detection of cold dust in the disks around two young BDs (CFHT-BD-Tau 4 and IC348 613), with deep JCMT and IRAM observations reaching flux levels of a few mJy. The dust masses are estimated to be a few Earth masses assuming the same dust opacities as usually applied to TTauri stars.Comment: 5 pages, accepted for ApJ

The CARMENES radial velocity (RV) survey is observing 324 M dwarfs to search for any orbiting planets. In this paper, we present the survey sample by publishing one CARMENES spectrum for each M dwarf. These spectra cover the wavelength range 520-1710 nm at a resolution of at least R > 80, 000, and we measure its RV, Hα emission, and projected rotation velocity. We present an atlas of high-resolution M-dwarf spectra and compare the spectra to atmospheric models. To quantify the RV precision that can be achieved in low-mass stars over the CARMENES wavelength range, we analyze our empirical information on the RV precision from more than 6500 observations. We compare our high-resolution M-dwarf spectra to atmospheric models where we determine the spectroscopic RV information content, Q, and signal-to-noise ratio. We find that for all M-type dwarfs, the highest RV precision can be reached in the wavelength range 700-900 nm. Observations at longer wavelengths are equally precise only at the very latest spectral types (M8 and M9). We demonstrate that in this spectroscopic range, the large amount of absorption features compensates for the intrinsic faintness of an M7 star. To reach an RV precision of 1 m s −1 in very low mass M dwarfs at longer wavelengths likely requires the use of a 10 m class telescope. For spectral types M6 and earlier, the combination of a red visual and a near-infrared spectrograph is ideal to search for low-mass planets and to distinguish between planets and stellar variability. At a 4 m class telescope, an instrument like CARMENES has the potential to push the RV precision well below the typical jitter level of 3-4 m s −1 .

Einc schr wichtigc Eigeiiscliaft selir junger iiiassereiclicr Sternc (BN-Objckte) 1st ilir intcnsivcr Massenvcrlust. Wir geben die wichtigsten Mcthoden a n , uin dic Mnssciiverlustratcii abzuleitcn. Bcobachtungsergcbiiissc wcrdcn vcrwcndct, uni die ionisicrtcn Sternwindc und dic CO-Fliisse zu charakterisieren. Dic Ergebnisse wcrden niit bestellenden Tlieoricn zuin Masscnverlust konfronticrt.A vcry important property of very young and massive stars (BN objects) is their iiitcnsive mass loss. We describe the main mcthods to derive tlie mass loss rates. Available observations arc used to characterize thc ionizcd stellar winds and the CO flows. The rcsults arc confronted with theories describing the anisotropic inass loss.

Our search for the earliest stages of massive star formation turned up 12 massive pre-protocluster candidates plus a few protoclusters. For this search, we selected 47 FIR-bright IRAS sources in the outer Galaxy. We mapped regions of several square arcminutes around the IRAS source in the millimeter continuum in order to find massive cold cloud cores possibly being in a very early stage of massive star formation. Masses and densities are derived for the 128 molecular cloud cores found in the obtained maps. We present these maps together with near-infrared, mid-infrared, and radio data collected from the 2MASS, MSX, and NVSS catalogs. Further data from the literature on detections of high-density tracers, outflows, and masers are added. The multiwavelength data sets are used to characterize each observed region. The massive cloud cores (M > 100 M ) are placed in a tentative evolutionary sequence depending on their emission at the investigated wavelengths. Candidates for the youngest stages of massive star formation are identified by the lack of detections in the above-mentioned near-infrared, mid-infrared, and radio surveys. Twelve massive cores prominent in the millimeter continuum fulfill this requirement. Since neither FIR nor radio emission have been detected from these cloud cores, massive protostars must be very deeply embedded in these cores. Some of these objects may actually be pre-protocluster cores: an up to now rare object class, where the initial conditions of massive star formation can be studied.