Search

We present a detailed analysis for a subset of the high-resolution (∼35 mas, or 5 au) ALMA observations from the Disk Substructures at High Angular Resolution Project (DSHARP) to search for faint 1.3 mm continuum emission associated with dusty circumplanetary material located within the narrow annuli of depleted emission (gaps) in circumstellar disks. This search used the Jennings et al. frank modeling methodology to mitigate contamination from the local disk emission and then deployed a suite of injection–recovery experiments to statistically characterize point-like circumplanetary disks in residual images. While there are a few putative candidates in this sample, they have only marginal local signal-to-noise ratios and would require deeper measurements to confirm. Associating a 50% recovery fraction with an upper limit, we find that these data are sensitive to circumplanetary disks with flux densities ≳50–70 μJy in most cases. There are a few examples where those limits are inflated (≳110 μJy) owing to lingering nonaxisymmetric structures in their host circumstellar disks, most notably for a newly identified faint spiral in the HD 143006 disk. For standard assumptions, this analysis suggests that these data should be sensitive to circumplanetary disks with dust masses. While those bounds are comparable to some theoretical expectations for young giant planets, we discuss how plausible system properties (e.g., relatively low host planet masses or the efficient radial drift of solids) could require much deeper observations to achieve robust detections. [ABSTRACT FROM AUTHOR]

We present Atacama Large Millimeter/submillimeter Array CO (J = 2–1) and 1.3 mm continuum observations of the high-velocity jet associated with the FIR 6b protostar located in the Orion Molecular Cloud-2. We detect a velocity gradient along the short axis of the jet in both the red- and blueshifted components. The position–velocity diagrams along the short axis of the redshifted jet show a typical characteristic of a rotating cylinder. We attribute the velocity gradient in the redshifted component to rotation of the jet. The rotation velocity (>20 km s−1) and specific angular momentum (>1022 cm2 s−1) of the jet around FIR 6b are the largest among all jets in which rotation has been observed. By combining disk wind theory with our observations, the jet launching radius is estimated to be in the range of 2.18–2.96 au. The rapid rotation, large specific angular momentum, and a launching radius far from the central protostar can be explained by a magnetohydrodynamic disk wind that contributes to the angular momentum transfer in the late stages of protostellar accretion. [ABSTRACT FROM AUTHOR]

We present high-resolution millimeter continuum and CO line observations for the circumbinary disk around V892 Tau to constrain the stellar and disk properties. The total mass of the two near-equal-mass A stars is estimated to be 6.0 ± 0.2 M⊙ based on our models of the Keplerian-dominated gas disk rotation. The detection of strong ionized gas emission associated with the two stars at 8 mm, when combined with previous astrometric measurements in the near-infrared, provides an updated view of the binary orbit with a = 7.1 ± 0.1 au, e = 0.27 ± 0.1, and P = 7.7 ± 0.2 yr, which is about half of a previously reported orbital period. The binary orbital plane is proposed to be nearly coplanar to the circumbinary disk plane (with a mutual inclination of only Δ = 8 ± 4.°2; another solution with Δ = 113° is less likely given the short realignment timescale). An asymmetric dust disk ring peaking at a radius of 0.″2 is detected at 1.3 mm and its fainter counterparts are also detected at the longer 8 and 9.8 mm. The CO gas disk, though dominated by Keplerian rotation, presents a mild inner and outer disk misalignment. The radial extension of the disk, its asymmetric dust ring, and the presence of a disk warp could all be explained by the interaction between the eccentric binary and the circumbinary disk, which we assume were formed with nonzero mutual inclination. Some tentatively detected gas spirals in the outer disk are likely produced by interactions with the low-mass tertiary component located 4″ to the northeast. Our analyses demonstrate the promising usage of V892 Tau as an excellent benchmark system to study the details of binary–disk interactions. [ABSTRACT FROM AUTHOR]

Utilizing the Atacama Large Millimeter/submillimeter Array, we present CS line maps in five rotational lines (Ju = 7, 5, 4, 3, 2) toward the circumnuclear disk (CND) and streamers of the Galactic center. Our primary goal is to resolve the compact structures within the CND and the streamers, in order to understand the stability conditions of molecular cores in the vicinity of the supermassive black hole (SMBH) Sgr A*. Our data provide the first homogeneous high-resolution (1.″3 = 0.05 pc) observations aiming at resolving density and temperature structures. The CS clouds have sizes of 0.05–0.2 pc with a broad range of velocity dispersion (σFWHM = 5–40 km s−1). The CS clouds are a mixture of warm (Tk ≥ 50–500 K, = 103–105 cm−3) and cold gas (Tk ≤ 50 K, = 106–108 cm−3). A stability analysis based on the unmagnetized virial theorem including tidal force shows that of the total gas mass is tidally stable, which accounts for the majority of gas mass. Turbulence dominates the internal energy and thereby sets the threshold densities 10–100 times higher than the tidal limit at distance ≥1.5 pc to Sgr A*, and therefore it inhibits the clouds from collapsing to form stars near the SMBH. However, within the central 1 pc, the tidal force overrides turbulence and the threshold densities for a gravitational collapse quickly grow to ≥ 108 cm−3. [ABSTRACT FROM AUTHOR]

A unique filament is identified in the Herschel maps of the Orion A giant molecular cloud. The filament, which we name the Stick, is ruler-straight and at an early evolutionary stage. Transverse position–velocity diagrams show two velocity components closing in on the Stick. The filament shows consecutive rings/forks in C18O (1−0) channel maps, which is reminiscent of structures generated by magnetic reconnection. We propose that the Stick formed via collision-induced magnetic reconnection (CMR). We use the magnetohydrodynamics code Athena++ to simulate the collision between two diffuse molecular clumps, each carrying an antiparallel magnetic field. The clump collision produces a narrow, straight, dense filament with a factor of >200 increase in density. The production of the dense gas is seven times faster than freefall collapse. The dense filament shows ring/fork-like structures in radiative transfer maps. Cores in the filament are confined by surface magnetic pressure. CMR can be an important dense-gas-producing mechanism in the Galaxy and beyond. [ABSTRACT FROM AUTHOR]

We present a spectroscopic survey of over 3400 potential members in the North America and Pelican Nebulae (NAP) using several low-resolution (R ≈ 1300–2000) spectrographs: Palomar/Norris, WIYN/Hydra, Keck/DEep Imaging Multi-Object Spectrograph (DEIMOS), and the Multiple Mirror Telescope (MMT)/Hectospec. We identify 580 young stars as likely members of the NAP region based on criteria involving infrared excess, Li I 6708 Å absorption, X-ray emission, parallax, and proper motions. The spectral types of individual spectra are derived by fitting them with templates that are either empirical spectra of pre-main-sequence stars or model atmospheres. The templates are artificially veiled, and a best-fit combination of spectral type and veiling parameter is derived for each star. We use the spectral types with archival photometry to derive V-band extinction and stellar luminosity. From the Hertzsprung–Russell diagram, the median age of the young stars is about 1 Myr, with a luminosity dispersion of ∼0.3–0.4 dex. We investigate the photometric variability of the spectroscopic member sample using Zwicky Transient Facility data and conclude that photometric variability, while present, does not significantly contribute to the luminosity dispersion. While larger than the formal errors, the luminosity dispersion is smaller than if veiling were not taken into account in our spectral typing process. The measured ages of the stellar kinematic groups, combined with the inferred ages for embedded stellar populations revealed by Spitzer, suggest a sequential history of star formation in the NAP region. [ABSTRACT FROM AUTHOR]

We examine the clustering and kinematics of young stellar objects (YSOs) in the North America/Pelican Nebulae, as revealed by Gaia astrometry, in relation to the structure and motions of the molecular gas, as indicated in molecular-line maps. The Gaia parallaxes and proper motions allow us to significantly refine previously published lists of YSOs, demonstrating that many of the objects previously thought to form a distributed population turn out to be nonmembers. The members are subdivided into at least six spatio-kinematic groups, each of which is associated with its own molecular cloud component or components. Three of the groups are expanding, with velocity gradients of 0.3–0.5 km s−1 pc−1, up to maximum velocities of ∼8 km s−1 away from the groups' centers. The two known O-type stars associated with the region, 2MASS J20555125+4352246 and HD 199579, are rapidly escaping one of these groups, following the same position–velocity relation as the low-mass stars. We calculate that a combination of gas expulsion and tidal forces from the clumpy distribution of molecular gas could impart the observed velocity gradients within the groups. However, on a global scale, the relative motions of the groups do not appear either divergent or convergent. The velocity dispersion of the whole system is consistent with the kinetic energy gained due to gravitational collapse of the complex. Most of the stellar population has ages similar to the freefall timescales for the natal clouds. Thus, we suggest the nearly freefall collapse of a turbulent molecular cloud as the most likely scenario for star formation in this complex. [ABSTRACT FROM AUTHOR]

The volatile composition of a planet is determined by the inventory of gas and ice in the parent disk. The volatile chemistry in the disk is expected to evolve over time, though this evolution is poorly constrained observationally. We present Atacama Large Millimeter/submillimeter Array observations of C18O, C2H, and the isotopologues H13CN, HC15N, and DCN toward five Class 0/I disk candidates. Combined with a sample of 14 Class II disks presented in Bergner et al., this data set offers a view of volatile chemical evolution over the disk lifetime. Our estimates of C18O abundances are consistent with a rapid depletion of CO in the first ∼0.5–1 Myr of the disk lifetime. We do not see evidence that C2H and HCN formation are enhanced by CO depletion, possibly because the gas is already quite under-abundant in CO. Further CO depletion may actually hinder their production by limiting the gas-phase carbon supply. The embedded sources show several chemical differences compared to the Class II stage, which seem to arise from shielding of radiation by the envelope (impacting C2H formation and HC15N fractionation) and sublimation of ices from infalling material (impacting HCN and C18O abundances). Such chemical differences between Class 0/I and Class II sources may affect the volatile composition of planet-forming material at different stages in the disk lifetime. [ABSTRACT FROM AUTHOR]

While protoplanetary disks often appear to be compact and well organized in millimeter continuum emission, CO spectral line observations are increasingly revealing complex behavior at large distances from the host star. We present deep Atacama Large Millimeter/submillimeter Array maps of the J = 2−1 transition of 12CO, 13CO, and C18O, as well as the J = 3−2 transition of DCO+, toward the T Tauri star RU Lup at a resolution of ∼0.3″ (∼50 au). The CO isotopologue emission traces four major components of the RU Lup system: a compact Keplerian disk with a radius of ∼120 au, a non-Keplerian "envelope-like" structure surrounding the disk and extending to ∼260 au from the star, at least five blueshifted spiral arms stretching up to 1000 au, and clumps outside the spiral arms located up to 1500 au in projection from RU Lup. We comment on potential explanations for RU Lup's peculiar gas morphology, including gravitational instability, accretion of material onto the disk, or perturbation by another star. RU Lup's extended non-Keplerian CO emission, elevated stellar accretion rate, and unusual photometric variability suggest that it could be a scaled-down Class II analog of the outbursting FU Ori systems. [ABSTRACT FROM AUTHOR]

We utilize ALMA archival data to estimate the dust disk size of 152 protoplanetary disks in Lupus (1–3 Myr), Chamaeleon I (2–3 Myr), and Upper-Sco (5–11 Myr). We combine our sample with 47 disks from Tau/Aur and Oph whose dust disk radii were estimated, as here, through fitting radial profile models to visibility data. We use these 199 homogeneously derived disk sizes to identify empirical disk–disk and disk–host property relations as well as to search for evolutionary trends. In agreement with previous studies, we find that dust disk sizes and millimeter luminosities are correlated, but show for the first time that the relationship is not universal between regions. We find that disks in the 2–3 Myr old Cha I are not smaller than disks in other regions of similar age, and confirm the Barenfeld et al. finding that the 5–10 Myr USco disks are smaller than disks belonging to younger regions. Finally, we find that the outer edge of the solar system, as defined by the Kuiper Belt, is consistent with a population of dust disk sizes which have not experienced significant truncation. [ABSTRACT FROM AUTHOR]

We report the discovery by the Palomar Transient Factory (PTF) of the transient source PTF11agg, which is distinguished by three primary characteristics: (1) bright (Rpeak = 18.3mag), rapidly fading (ΔR = 4mag inΔt = 2 days) optical transient emission; (2) a faint (R = 26.2 ± 0.2mag), blue (g' − R = 0.17 ± 0.29 mag)quiescent optical counterpart; and (3) an associated year-long, scintillating radio transient. We argue that the seobserved properties are inconsistent with any known class of Galactic transients (flare stars, X-ray binaries, dwarf novae), and instead suggest a cosmological origin. The detection of incoherent radio emission at such distance simplies a large emitting region, from which we infer the presence of relativistic ejecta. The observed properties areall consistent with the population of long-duration gamma-ray bursts (GRBs), marking the first time such an outburst has been discovered in the distant universe independent of a high-energy trigger. We searched for possible high energy counter parts to PTF11agg, but found no evidence for associated prompt emission. We therefore consider three possible scenarios to account for a GRB-like after glow without a high-energy counterpart: an “untriggered”GRB (lack of satellite coverage), an “orphan” afterglow (viewing-angle effects), and a “dirty fireball” (suppressed high-energy emission). The observed optical and radio light curves appear inconsistent with even the most basic predictions for off-axis afterglow models. The simplest explanation, then, is that PTF11agg is a normal, on-axislong-duration GRB for which the associated high-energy emission was simplymissed. However, we have calculated the likelihood of such a serendipitous discovery by PTF and find that it is quite small (≈2.6%). While not definitive,we nonetheless speculate that PTF11agg may represent a new, more common (>4 times the on-axis GRB rate at 90% confidence) class of relativistic outbursts lacking associated high-energy emission. If so, such sources will be uncovered in large numbers by future wide-field optical and radio transient surveys. [ABSTRACT FROM AUTHOR]

We present results of λ1.3 mm dust-polarization observations toward 16 nearby, low-mass protostars, mapped with ~2''. 5 resolution at CARMA. The results show that magnetic fields in protostellar cores on scales of ~1000 AU are not tightly aligned with outflows from the protostars. Rather, the data are consistent with scenarios where outflows and magnetic fields are preferentially misaligned (perpendicular), or where they are randomly aligned. If one assumes that outflows emerge along the rotation axes of circumstellar disks, and that the outflows have not disrupted the fields in the surrounding material, then our results imply that the disks are not aligned with the fields in the cores from which they formed. [ABSTRACT FROM AUTHOR]

Clumpy structure in the debris disk around Vega has been previously reported at millimeter wavelengths and attributed to concentrations of dust grains trapped in resonances with an unseen planet. However, recent imaging at similar wavelengths with higher sensitivity has disputed the observed structure. We present three new millimeter-wavelength observations that help to resolve the puzzling and contradictory observations. We have observed the Vega system with the Submillimeter Array (SMA) at a wavelength of 880 µm and an angular resolution of 5″; with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) at a wavelength of 1.3 mm and an angular resolution of 5″; and with the Green Bank Telescope (GBT) at a wavelength of 3.3 mm and angular resolution of 10″. Despite high sensitivity and short baselines, we do not detect the Vega debris disk in either of the interferometric data sets (SMA and CARMA), which should be sensitive at high significance to clumpy structure based on previously reported observations. We obtain a marginal (3σ) detection of disk emission in the GBT data; the spatial distribution of the emission is not well constrained. We analyze the observations in the context of several different models, demonstrating that the observations are consistent with a smooth, broad, axisymmetric disk with inner radius 20-100 AU and width ≳50 AU. The interferometric data require that at least half of the 860 µm emission detected by previous single-dish observations with the James Clerk Maxwell Telescope be distributed axisymmetrically, ruling out strong contributions from flux concentrations on spatial scales of ≳100 AU. These observations support recent results from the Plateau de Bure Interferometer indicating that previous detections of clumpy structure in the Vega debris disk were spurious. [ABSTRACT FROM AUTHOR]

We present the Combined Array for Research in Millimeter-wave Astronomy (CARMA) observations of the three northern unconfirmed galaxy clusters discovered by the Planck satellite. We confirm the existence of two massive clusters (PLCKESZ G115.71+17.52 and PLCKESZ G121.11+57.01) at high significance. For these clusters, we present refined centroid locations from the 31 GHz CARMA data, as well as mass estimates obtained from a joint analysis of CARMA and Planck data. We do not detect the third candidate, PLCKESZ G189.84-37.24, and place an upper limit on its mass of M500 <3.2 x 1014 M⊙ at 68% confidence. Considering our data and the characteristics of the Planck Early Sunyaev-Zel'dovich (ESZ) Catalog, we conclude that this object is likely to be a cold-core object in the plane of our Galaxy. As a result, we estimate the purity of the ESZ Catalog to be greater than 99.5%. [ABSTRACT FROM AUTHOR]

We present Combined Array for Research in Millimeter-wave Astronomy 1.3 mm continuum observations of the T Tauri star LkCa 15, which resolve the circumstellar dust continuum emission on angular scales between 0".2 and 3", corresponding to 28-420 AU at the distance of the star. The observations resolve the inner gap in the dust emission and reveal an asymmetric dust distribution in the outer disk. By comparing the observations with theoretical disk models, we calculate that 90% of the dust emission arises from an azimuthally symmetric ring that contains about 5 x 10-4 M⊙ of dust. A low surface-brightness tail that extends to the northwest out to a radius of about 300 AU contains the remaining 10% of the observed continuum emission. The ring is modeled with a rather flat surface density profile between 40 and 120 AU, while the inner cavity is consistent with either a sharp drop of the 1.3 mm dust optical depth at about 42 AU or a smooth inward decrease between 3 and 85 AU. We show that early science Atacama Large Millimeter Array observations will be able to disentangle these two scenarios. Within 40 AU, the observations constrain the amount of dust between 10-6 and 7 Earth masses, where the minimum and maximum limits are set by the near-infrared spectral energy distribution modeling and by the millimeter-wave observations of the dust emission, respectively. In addition, we confirm the discrepancy in the outer disk radius inferred from the dust and gas, which corresponds to 150 AU and 900 AU, respectively. We cannot reconcile this difference by adopting an exponentially tapered surface density profile as suggested for other systems, but we instead suggest that the gas surface density in the outer disk decreases less steeply than that predicted by model fits to the dust continuum emission. The lack of continuum emission at radii larger than 120 AU suggests a drop of at least a factor of five in the dust-to-gas ratio or in the dust opacity. We show that a sharp dust opacity drop of this magnitude is consistent with a radial variation of the grain size distribution as predicted by existing grain growth models. [ABSTRACT FROM AUTHOR]

On 2011 August 24 (UT) the Palomar Transient Factory (PTF) discovered PTF11kly (SN 2011fe), the youngest and most nearby Type Ia supernova (SN Ia) in decades. We followed this event up in the radio (centimeter and millimeter bands) and X-ray bands, starting about a day after the estimated explosion time. We present our analysis of the radio and X-ray observations, yielding the tightest constraints yet placed on the pre-explosion mass-loss rate from the progenitor system of this supernova. We find a robust limit of M ≲ 10-8(w/100 km s-1) M⊙ yr-1 from sensitive X-ray non-detections, as well as a similar limit from radio data, which depends, however, on assumptions about microphysical parameters. We discuss our results in the context of single-degenerate models for SNe Ia and find that our observations modestly disfavor symbiotic progenitor models involving a red giant donor, but cannot constrain systems accreting from main-sequence or sub-giant stars, including the popular supersoft channel. In view of the proximity of PTF11kly and the sensitivity of our prompt observations, we would have to wait for a long time (a decade or longer) in order to more meaningfully probe the circumstellar matter of SNe Ia. [ABSTRACT FROM AUTHOR]

We present ALMA observations of the 880 μm continuum and CO J = 3-2 line emission from the transition disk around [PZ99] J160421.7-213028, a solar mass star in the Upper Scorpius OB association. Analysis of the continuum data indicates that 80% of the dust mass is concentrated in an annulus extending between 79 and 114 AU in radius. Dust is robustly detected inside the annulus, at a mass surface density 100 times lower than that at 80 AU. The CO emission in the inner disk also shows a significantly decreased mass surface density, but we infer a cavity radius of only 31 AU for the gas. The large separation of the dust and gas cavity edges, as well as the high radial concentration of millimeter-sized dust grains, is qualitatively consistent with the predictions of pressure trap models that include hydrodynamical disk-planet interactions and dust coagulation/fragmentation processes. [ABSTRACT FROM AUTHOR]

We present Karl G. Jansky Very Large Array (VLA) observations of the 7 mm continuum emission from the disk surrounding the young star LkCa 15. The observations achieve an angular resolution of 70 mas and spatially resolve the circumstellar emission on a spatial scale of 9 AU. The continuum emission traces a dusty annulus of 45 AU in radius that is consistent with the dust morphology observed at shorter wavelengths. The VLA observations also reveal a compact source at the center of the disk, possibly due to thermal emission from hot dust or ionized gas located within a few AU from the central star. No emission is observed between the star and the dusty ring and, in particular, at the position of the candidate protoplanet LkCa 15 b. By comparing the observations with theoretical models for circumplanetary disk emission, we find that if LkCa 15 b is a massive planet (>5 MJ) accreting at a rate greater than 10–6MJ yr–1, then its circumplanetary disk is less massive than 0.1 MJ, or smaller than 0.4 Hill radii. Similar constraints are derived for any possible circumplanetary disk orbiting within 45 AU from the central star. The mass estimates are uncertain by at least one order of magnitude due to the uncertainties on the mass opacity. Future ALMA observations of this system might be able to detect circumplanetary disks down to a mass of 5 × 10–4MJ and as small as 0.2 AU, providing crucial constraints on the presence of giant planets in the act of forming around this young star. [ABSTRACT FROM AUTHOR]

We present ALMA 880 μm continuum observations of 20 K- and M-type stars in the Upper Scorpius OB association (Upper Sco) that are surrounded by protoplanetary disks. These data are used to measure the dust content in disks around low-mass stars (0.1-1.6 M☼) at a stellar age of 5-11 Myr. Thirteen sources were detected in the 880 μm dust continuum at ⩾3σ with inferred dust masses between 0.3 and 52 M⊕. The dust masses tend to be higher around the more massive stars, but the significance is marginal in that the probability of no correlation is p ≈ 0.03. The evolution in the dust content in disks was assessed by comparing the Upper Sco observations with published continuum measurements of disks around ∼1-2 Myr stars in the Class II stage in the Taurus molecular cloud. While the dust masses in the Upper Sco disks are on average lower than in Taurus, any difference in the dust mass distributions is significant at less than 3σ. For stellar masses between 0.49 M☼ and 1.6 M☼, the mean dust mass in disks is lower in Upper Sco relative to Taurus by Δlog Mdust = 0.44 ± 0.26. [ABSTRACT FROM AUTHOR]

The companion to the G0V star HR7672 directly imaged by Liu et al. has moved measurably along its orbit since the discovery epoch, making it possible to determine its dynamical properties. Originally targeted with adaptive optics because it showed a long-term radial velocity (RV) acceleration (trend), we have monitored this star with precise Doppler measurements and have now established a 24 year time baseline. The RV variations show significant curvature (change in the acceleration) including an inflection point. We have also obtained a recent image of HR7672B with NIRC2 at Keck. The astrometry also shows curvature. In this paper, we use jointly fitted Doppler and astrometric models to calculate the three-dimensional orbit and dynamical mass of the companion. The mass of the host star is determined using a direct radius measurement from CHARA interferometry in combination with high-resolution spectroscopic modeling. We find that HR7672B has a highly eccentric, e = 0.50+0.01–0.01, near edge-on, i = 97.3+0.4–0.5 deg, orbit with semimajor axis, a = 18.3+0.4–0.5 AU. The mass of the companion is m = 68.7+2.4–3.1MJ. HR7672B thus resides near the substellar boundary, just below the hydrogen-fusing limit. These measurements of the companion mass are independent of its brightness and spectrum and establish HR7672B as a rare and precious “benchmark” brown dwarf with a well-determined mass, age, and metallicity essential for testing theoretical evolutionary models and synthetic spectral models. Indeed, we find that such models under-predict its luminosity by a factor of ≈2. HR 7672B is presently the only L, T, or Y dwarf known to produce an RV trend around a solar-type star. [ABSTRACT FROM AUTHOR]