Context. The Ophiuchus clouds, in particular L 1688, are an excellent region to study the embedded phases of star formation, due to the relatively large number of protostars. However, the standard method of finding and characterizing embedded young stellar objects (YSOs) through just their infrared spectral slope does not yield a reliable sample. This may affect the age determinations, often derived from the statistics on the total number of embedded YSOs and pre-main sequence stars within a cloud. Aims. Our aim is to characterize the structure of protostellar envelopes on an individual basis and to correctly identify the embedded YSO population of L 1688. Methods. Spectral maps of the HCO + J = 4−3 and C 18 O J = 3−2 lines, using the HARP-B array on the James Clerk Maxwell Telescope and SCUBA 850 μm dust maps, are obtained of all sources in the L 1688 region with infrared spectral slopes consistent with, or close to, that of embedded YSOs. Selected 350 μm maps obtained with the Caltech Submillimeter Observatory are presented as well. The properties, extent and variation of dense gas, column density and dust up to 1 (∼7500 AU) are probed at 15 resolution. Using the spatial variation of the gas and dust, together with the intensity of the HCO + J = 4−3 line, we are able to accurately identify the truly embedded YSOs and determine their properties. Results. The protostellar envelopes range from 0.05 to 0.5 M in mass. The concentration of HCO + emission (∼0.5 to 0.9) is generally higher than that of the dust concentration. Combined with absolute intensities, HCO + proves to be a better tracer of protostellar envelopes than dust, which can contain disk and cloud contributions. Our total sample of 45 sources, including all previously classified Class I sources, several flat-spectrum sources and some known disks, was re-classified using the molecular emission. Of these, only 17 sources are definitely embedded YSOs. Four of these embedded YSOs have little (0.1−0.2 M ) envelope material remaining and are likely at the interesting transitional stage from embedded YSO to T Tauri star. About half of the flat-spectrum sources are found to be embedded YSOs and about half are disks. Conclusions. The presented classification method is successful in separating embedded YSOs from edge-on disks and confused sources. The total embedded population of the Ophiuchus L 1688 cloud is found almost exclusively in Oph-A, Oph-B2 and the Ophiuchus ridge with only three embedded YSOs not related to these regions. The detailed characterization presented will be necessary to interpret deep interferometric ALMA and future Herschel observations.

Astrophysics ABSTRACTContext. Young stars are formed with dusty discs around them. The dust grains in the disc are originally of the same size as interstellar dust, i.e., of the order of 0.1 μm. Models predict that these grains will grow in size through coagulation. Observations of the silicate features around 10 and 20 μm are consistent with growth from submicron to micron sizes in selected sources whereas the slope of the spectral energy distribution (SED) at mm and cm wavelengths traces growth up to mm sizes and larger. Aims. We here look for a correlation between these two grain growth indicators. Methods. A large sample of T-Tauri and Herbig-Ae/Be stars, spread over the star-forming regions in Chamaeleon, Lupus, Serpens, Corona Australis, and the Gum nebula in Vela, was observed with the Spitzer Space Telescope at 5−13 μm, and a subsample was observed with the SMA, ATCA, CARMA, and VLA at mm wavelengths. We complement this subsample with data from the literature to maximise the overlap between μm and mm observations and search for correlations in the grain-growth signatures. Synthetic spectra are produced to determine which processes may produce the dust evolution observed in protoplanetary discs. Results. Dust disc masses in the range <1 to 7 × 10 −4 M are obtained. The majority of the sources have a mm spectral slope consistent with grain growth. There is a tentative correlation between the strength and the shape of the 10-μm silicate feature and the slope of the SED between 1 and 3 mm. The observed sources seem to be grouped per star-forming region in the 10-μm-feature vs. mmslope diagram. The modelling results show that, if only the maximum grain size is increased, first the 10-μm feature becomes flatter and subsequently the mm slope becomes shallower. To explain the sources with the shallowest mm slopes, a grain size distribution shallower than that of the interstellar medium is required. Furthermore, the strongest 10-μm features can only be explained with bright (L ∼ 6 L ), hot (T eff = 4000 K) central stars. Settling of larger grains towards the disc midplane results in a stronger 10-μm feature, but has a very limited effect on the mm slope. Conclusions. A tentative correlation between the strength of the 10-μm feature and the mm slope is found, which would imply that the inner and outer disc evolve simultaneously. Dust with a mass dominated by large, ∼mm-sized, grains is required to explain the shallowest mm slopes. Other processes besides grain growth, such as the clearing of an inner disc by binary interaction, may also be responsible for the removal of small grains. Observations with future telescopes with larger bandwidths or collecting areas are required to provide the necessary statistics to study these processes of disc and dust evolution.

We present observations of N 2 H + (J = 1 → 0), HCO + (J = 1 → 0), and HCN (J = 1 → 0) toward the Serpens Main molecular cloud from the CARMA Large Area Star Formation Survey (CLASSy). We mapped 150 square arcminutes of Serpens Main with an angular resolution of ∼ 7 . The gas emission is concentrated in two subclusters (the NW and SE subclusters). The SE subcluster has more prominent filamentary structures and more complicated kinematics compared to the NW subcluster. The majority of gas in the two subclusters has subsonic to sonic velocity dispersions. We applied a dendrogram technique with N 2 H + (1-0) to study the gas structures; the SE subcluster has a higher degree of hierarchy than the NW subcluster. Combining the dendrogram -2and line fitting analyses reveals two distinct relations: a flat relation between nonthermal velocity dispersion and size, and a positive correlation between variation in velocity centroids and size. The two relations imply a characteristic depth of 0.15 pc for the cloud. Furthermore, we have identified six filaments in the SE subcluster. These filaments have lengths of ∼ 0.2 pc and widths of ∼ 0.03 pc, which is smaller than a characteristic width of 0.1 pc suggested by Herschel observations. The filaments can be classified into two types based on their properties. The first type, located in the northeast of the SE subcluster, has larger velocity gradients, smaller masses, and nearly critical mass-per-unit-length ratios. The other type, located in the southwest of the SE subcluster, has the opposite properties. Several YSOs are formed along two filaments which have supercritical mass per unit length ratios, while filaments with nearly critical mass-per-unit-length ratios are not associated with YSOs, suggesting that stars are formed on gravitationally unstable filaments.formation. The target regions, NGC 1333, Barnard 1, and L1451 in Perseus, and Serpens Main and Serpens South, present a wide range of star formation activities from relatively quiescent regions to active star-forming clusters. Storm et al. (2014) (hereafter Paper I) presents a detailed description on the CLASSy project and the structures of dense gas in Barnard 1. In this paper, we present results of the Serpens Main region. We focus on the global structure of dust and gas, including the properties of dust and gas condensations, gas structures and kinematics, and filamentary structures.

Observations of the T Tauri spectroscopic binary DQ Tau in April 2008 captured an unusual flare at 3 mm, which peaked at an observed maximum flux of ∼0.5 Jy (about 27 times the quiescent value). Here we present follow-up millimeter observations that demonstrate a periodicity to the phenomenon. While monitoring 3 new periastron encounters, we have detected flares within 17.5 h (or 4.6%) of the orbital phase of the first reported flare and constrained the main emitting region to a stellar height of 3.7-6.8 R . The recorded activity is consistent with the proposed picture for synchrotron emission initiated by a magnetic reconnection event when the two stellar magnetospheres of the highly eccentric (e = 0.556) binary are believed to collide near periastron as the stars approach a minimum separation of 8 R (∼13 R ). The similar light curve decay profiles allow us to estimate an average flare duration of 30 h. Assuming one millimeter flare per orbit, DQ Tau could spend approximately 8% of its 15.8-day orbital period in an elevated flux state. These findings continue to serve as a small caution for millimeter flux points in spectral energy distributions that could contain unrecognized flare contributions. Our analysis of the millimeter emission provides an upper limit of 5% on the linear polarization. We discuss the extent to which a severely entangled magnetic field structure and Faraday rotation effects are likely to reduce the observed polarization fraction. We also predict that, for the current picture, the stellar magnetospheres must be misaligned at a significant angle or, alternatively, that the topologies of the outer magnetospheres are poorly described by a well-ordered dipole inside a radius of 7 R . Finally, to investigate whether reorganization of the magnetic field during the interaction affects mass accretion, we also present simultaneous optical (VRI) monitoring of the binary, as an established tracer of accretion activity in this system. We find that an accretion event can occur coincident in both time and duration with the synchrotron fallout of a magnetic reconnection event. While the pulsed accretion mechanism has been attributed previously to the dynamical motions of the stars alone, the similarities between the millimeter and optical light curves evoke the possibility of a causal or co-dependent relationship between the magnetospheric and dynamical processes.

The young high-eccentricity binary DQ Tau exhibits powerful recurring millimeter-band (mm) flaring attributed to collisions between the two stellar magnetospheres near periastron, when the stars are separated by only ∼ 8 R ⋆ . These magnetospheric interactions are expected to have scales and magnetic field strengths comparable to those of large X-ray flares from single pre-mainsequence (PMS) stars observed in the Chandra Orion Ultradeep Project (COUP). To search for X-rays arising from processes associated with colliding magnetospheres, we performed simultaneous X-ray and mm observations of DQ Tau near periastron phase. We report here several results. 1) As anticipated, DQ Tau was caught in a flare state in both mm and X-rays. A single long X-ray flare spanned the entire 16.5 hour Chandra exposure. 2) The inferred morphology, duration, and plasma temperature of the X-ray flare are typical of those of large flares from COUP stars. 3) However, our study provides three lines of evidence that this X-ray flare likely arises from colliding magnetospheres: the chance of capturing a large COUP-like flare within the span of our observation is small; the relative timing of the X-ray and mm flares indicates the Neupert effect and is consistent with a common coronal structure; the size of the emitting coronal structure (4 − 5 R ⋆ ) inferred from our analysis (which is admittedly model-dependent and should be considered with caution) is comparable to half the binary separation. 4) The peak flare X-ray luminosity is in agreement with an estimate of the power dissipated by magnetic reconnection within the framework of a simple model of interacting magnetospheres.Subject headings: open clusters and associations: individual (DQ Tau) -stars: flare -stars: pre-main-sequence -X-rays: stars 5 The SAS Threads are available at