ALMA Observations of the Young Substellar Binary System 2M1207

We present ALMA observations of the 2M1207 system, a young binary made of a brown dwarf with a planetary-mass companion at a projected separation of about 40 au. We detect emission from dust continuum at 0.89 mm and from the $J = 3 - 2$ rotational transition of CO from a very compact disk around the young brown dwarf. The small radius found for this brown dwarf disk may be due to truncation from the tidal interaction with the planetary-mass companion. Under the assumption of optically thin dust emission, we estimated a dust mass of 0.1 $M_{\oplus}$ for the 2M1207A disk, and a 3$\sigma$ upper limit of $\sim 1~M_{\rm{Moon}}$ for dust surrounding 2M1207b, which is the tightest upper limit obtained so far for the mass of dust particles surrounding a young planetary-mass companion. We discuss the impact of this and other non-detections of young planetary-mass companions for models of planet formation, which predict the presence of circum-planetary material surrounding these objects.Comment: 10 pages, 6 figures, accepted for publication in A

Using Protoplanetary Disks To Weigh The Youngest Stars And Constrain The Earliest Stages Of Stellar Evolution

Mass is the fundamental property that determines the fate of a star. In particular, the masses of young stars are of great relevance to many astrophysical problems, including star and planet formation. We have developed a novel approach that combines spatially resolved sub-millimeter spectral line imaging and optical/near-infrared high resolution spectroscopy to derive the fundamental properties of a young star: mass, temperature, and radius. By applying our technique to a sample of pre-main sequence stars, we are mapping out a dynamically-calibrated Hertzsprung-Russell diagram for the express purpose of evaluating pre-main sequence evolutionary models. Looking forward, ALMA is poised to deliver precise stellar masses in statistically large quantities, enabling a meaningful survey of the fundamental properties of young stars

A disk-based dynamical mass estimate for the young binary AK Sco

Funding: I.C. is supported by the NSF Graduate Fellowship and the Smithsonian Institution.We present spatially and spectrally resolved Atacama Large Millimeter / submillimeter Array (ALMA) observations of gas and dust in the disk orbiting the pre-main sequence (pre-MS) binary AK Sco. By forward-modeling the disk velocity field traced by CO J = 2–1 line emission, we infer the mass of the central binary, M* = 2.49 ± 0.10 M⊙, a new dynamical measurement that is independent of stellar evolutionary models. Assuming the disk and binary are co-planar within ∼2°, this disk-based binary mass measurement is in excellent agreement with constraints from radial velocity monitoring of the combined stellar spectra. These ALMA results are also compared with the standard approach of estimating masses from the location of the binary in the Hertzsprung–Russell diagram, using several common pre-MS model grids. These models predict stellar masses that are marginally consistent with our dynamical measurement (at ∼2σ), but are systematically high (by ∼10%). These same models consistently predict an age of 18 ± 1 Myr for AK Sco, in line with its membership in the Upper Centaurus–Lupus association but surprisingly old for it to still host a gas-rich disk. As ALMA accumulates comparable data for large samples of pre-MS stars, the methodology employed here to extract a dynamical mass from the disk rotation curve should prove extraordinarily useful for efforts to characterize the fundamental parameters of early stellar evolution.Peer reviewe

Detecting weak spectral lines in interferometric data through matched filtering

Funding: R.A.L. and J.H. gratefully acknowledge funding from National Science Foundation Graduate Research Fellowships (Grant No. DGE-1144152). R.A.L. also acknowledges funding from the NRAO Student Observing Support Program. K.I.Ö. acknowledges funding from the Alfred P. Sloan Foundation and the David and Lucile Packard Foundation. C.W. acknowledges financial support from the Netherlands Organisation for Scientific Research (NWO, grant 639.041.335) and start-up funds from the University of Leeds, UK.Modern radio interferometers enable observations of spectral lines with unprecedented spatial resolution and sensitivity. In spite of these technical advances, many lines of interest are still at best weakly detected and therefore necessitate detection and analysis techniques specialized for the low signal-to-noise ratio (S/N) regime. Matched filters can leverage knowledge of the source structure and kinematics to increase sensitivity of spectral line observations. Application of the filter in the native Fourier domain improves S/N while simultaneously avoiding the computational cost and ambiguities associated with imaging, making matched filtering a fast and robust method for weak spectral line detection. We demonstrate how an approximate matched filter can be constructed from a previously observed line or from a model of the source, and we show how this filter can be used to robustly infer a detection significance for weak spectral lines. When applied to ALMA Cycle 2 observations of CH3OH in the protoplanetary disk around TW Hya, the technique yields a ≈53% S/N boost over aperture-based spectral extraction methods, and we show that an even higher boost will be achieved for observations at higher spatial resolution. A Python-based open-source implementation of this technique is available under the MIT license at http://github.com/AstroChem/VISIBLE.Publisher PDFPeer reviewe

The coupled physical structure of gas and dust in the IM Lup protoplanetary disk

Funding: IC gratefully acknowledges funding support from the Smithsonian Institution.The spatial distribution of gas and solids in protoplanetary disks determines the composition and formation efficiency of planetary systems. A number of disks show starkly different distributions for the gas and small grains compared to millimeter-centimeter-sized dust. We present new Atacama Large Millimeter/Submillimeter Array observations of the dust continuum, CO, 13CO, and C18O in the IM Lup protoplanetary disk, one of the first systems where this dust-gas dichotomy was clearly seen. The 12CO is detected out to a radius of 970 au, while the millimeter continuum emission is truncated at just 313 au. Based upon these data, we have built a comprehensive physical and chemical model for the disk structure, which takes into account the complex, coupled nature of the gas and dust and the interplay between the local and external environment. We constrain the distributions of gas and dust, the gas temperatures, the CO abundances, the CO optical depths, and the incident external radiation field. We find that the reduction/removal of dust from the outer disk exposes this region to higher stellar and external radiation and decreases the rate of freeze-out, allowing CO to remain in the gas out to large radial distances. We estimate a gas-phase CO abundance of 5% of the interstellar medium value and a low external radiation field (G 0 ≲ 4). The latter is consistent with that expected from the local stellar population. We additionally find tentative evidence for ring-like continuum substructure, suggestions of isotope-selective photodissociation, and a diffuse gas halo.Peer reviewe

The Degree Of Alignment Between Circumbinary Disks And Their Binary Hosts

All four circumbinary (CB) protoplanetary disks orbiting short-period (P \u3c 20 days) double-lined spectroscopic binaries (SB2s)—a group that includes UZ Tau E, for which we present new Atacama Large Millimeter/Submillimeter Array data—exhibit sky-plane inclinations i disk that match, to within a few degrees, the sky-plane inclinations i★ of their stellar hosts. Although for these systems the true mutual inclinations θ between disk and binary cannot be directly measured because relative nodal angles are unknown, the near coincidence of i disk and i★ suggests that θ is small for these most compact of systems. We confirm this hypothesis using a hierarchical Bayesian analysis, showing that 68% of CB disks around short-period SB2s have θ \u3c 30. Near coplanarity of CB disks implies near coplanarity of CB planets discovered by Kepler, which in turn implies that the occurrence rate of close-in CB planets is similar to that around single stars. By contrast, at longer periods ranging from 30 to 105 days (where the nodal degeneracy can be broken via, e.g., binary astrometry), CB disks exhibit a wide range of mutual inclinations, from coplanar to polar. Many of these long-period binaries are eccentric, as their component stars are too far separated to be tidally circularized. We discuss how theories of binary formation and disk–binary gravitational interactions can accommodate all these observations

A disk-based dynamical constraint on the mass of the young binary DQ Tau

Funding: I.C. gratefully acknowledges funding support from the Smithsonian Institution. S.A. appreciates the very helpful support provided by the NRAO Student Observing Support program related to the early development of this project.We present new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of CO J = 2-1 line emission from the DQ Tau circumbinary disk. These data are used to tomographically reconstruct the Keplerian disk velocity field in a forward-modeling inference framework, and thereby provide a dynamical constraint on the mass of the DQ Tau binary of M = 1.27-0.27+0.46 M⊙. Those results are compared with an updated and improved orbital solution for this double-lined system based on long-term monitoring of its stellar radial velocities. Both of these independent dynamical constraints on the binary mass are in excellent agreement: taken together, they demonstrate that the DQ Tau system mass is 1.21 ± 0.26 M⊙ and that the disk and binary orbital planes are aligned within 3° (at 3σ confidence). The predictions of various theoretical models for pre-main-sequence stellar evolution are also consistent with these masses, though more detailed comparisons are difficult due to lingering uncertainties regarding the photospheric properties of the individual components. DQ Tau is the third, nearly equal-mass, double-lined spectroscopic binary with a circumbinary disk that has been dynamically “weighed” with these two independent techniques: all show consistent results, validating the overall accuracy of the disk-based approach and demonstrating that it can be robustly applied to large samples of young, single stars as ALMA ramps up to operations at full capacity.Publisher PDFPeer reviewe

The intermediate luminosity optical transient SN 2010da : the progenitor, eruption, and aftermath of a peculiar supergiant high-mass X-ray binary

We present optical spectroscopy, ultraviolet-to-infrared imaging, and X-ray observations of the intermediate luminosity optical transient (ILOT) SN 2010da in NGC 300 (d = 1.86 Mpc) spanning from −6 to +6 years relative to the time of outburst in 2010. Based on the light-curve and multi-epoch spectral energy distributions of SN 2010da, we conclude that the progenitor of SN 2010da is a ≈10–12 M⊙ yellow supergiant possibly transitioning into a blue-loop phase. During outburst, SN 2010da had a peak absolute magnitude of Mbol ≲ −10.4 mag, dimmer than other ILOTs and supernova impostors. We detect multi-component hydrogen Balmer, Paschen, and Ca ii emission lines in our high-resolution spectra, which indicate a dusty and complex circumstellar environment. Since the 2010 eruption, the star has brightened by a factor of ≈5 and remains highly variable in the optical. Furthermore, we detect SN 2010da in archival Swift and Chandra observations as an ultraluminous X-ray source (LX ≈ 6 × 1039 erg s−1). We additionally attribute He ii 4686 Å and coronal Fe emission lines in addition to a steady X-ray luminosity of ≈1037 erg s−1 to the presence of a compact companion.Peer reviewe

ALMA observations of the young substellar binary system 2M1207

Funding: J.M.C. acknowledges support from the National Aeronautics and Space Administration under Grant No. 15XRP15_20140 issued through the Exoplanets Research Program. Support for this work was provided by NASA through Hubble Fellowship grant HST-HF2-51369.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555.We present ALMA observations of the 2M1207 system, a young binary made of a brown dwarf with a planetary-mass companion at a projected separation of about 40 au. We detect emission from dust continuum at 0.89 mm and from the J=3-2 rotational transition of CO from a very compact disk around the young brown dwarf. The small radius found for this brown dwarf disk may be due to truncation from the tidal interaction with the planetary-mass companion. Under the assumption of optically thin dust emission, we estimate a dust mass of 0.1 M ⊕ for the 2M1207A disk and a 3σ upper limit of ∼1 MMoon for dust surrounding 2M1207b, which is the tightest upper limit obtained so far for the mass of dust particles surrounding a young planetary-mass companion. We discuss the impact of this and other non-detections of young planetary-mass companions for models of planet formation that predict circumplanetary material to surround these objects.Publisher PDFPeer reviewe

Detecting Weak Spectral Lines in Interferometric Data through Matched Filtering

Modern radio interferometers enable observations of spectral lines with unprecedented spatial resolution and sensitivity. In spite of these technical advances, many lines of interest are still at best weakly detected and therefore necessitate detection and analysis techniques specialized for the low signal-to-noise ratio (S/N) regime. Matched filters can leverage knowledge of the source structure and kinematics to increase sensitivity of spectral line observations. Application of the filter in the native Fourier domain improves S/N while simultaneously avoiding the computational cost and ambiguities associated with imaging, making matched filtering a fast and robust method for weak spectral line detection. We demonstrate how an approximate matched filter can be constructed from a previously observed line or from a model of the source, and we show how this filter can be used to robustly infer a detection significance for weak spectral lines. When applied to ALMA Cycle 2 observations of CH3OH in the protoplanetary disk around TW Hya, the technique yields a ≈53% S/N boost over aperture-based spectral extraction methods, and we show that an even higher boost will be achieved for observations at higher spatial resolution. A Python-based open-source implementation of this technique is available under the MIT license at http://github.com/AstroChem/VISIBLE