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NASA NTRS2020

Evidence for Magnetic Activity at Starbirth: a Powerful X-ray Flare From the Class 0 Protostar HOPS 383

Context. Class 0 protostars represent the earliest evolutionary stage of solar-type stars, during which the majority of the system mass resides in an infalling envelope of gas and dust and not yet in the central, nascent star. Although X-rays are a key signature of magnetic activity in more evolved protostars and young stars, whether such magnetic activity is present at the Class 0 stage is still debated. Aims. We aim to detect a bona fide Class 0 protostar in X-rays. Methods. We observed HOPS 383 in 2017 December in X-rays with the Chandra X-ray Observatory (~84 ks) and in near-infrared imaging with the Southern Astrophysical Research Telescope (SOAR). Results. HOPS 383 was detected in X-rays during a powerful flare. This hard (E > 2 keV) X-ray counterpart was spatially coincident with the northwest 4-cm component of HOPS 383, which would be the base of the radio thermal jet launched by HOPS 383. The flare duration was ~3.3 h; at the peak, the X-ray luminosity reached ~4 x 10(exp 31) erg/s in the 2–8 keV energy band, a level at least an order of magnitude larger than that of the undetected quiescent emission from HOPS 383. The X-ray flare spectrum is highly absorbed (N(H) ~ 7 x 10(exp 23) per sq.cm), and displays a 6.4 keV emission line with an equivalent width of ~1:1 keV, arising from neutral or low-ionization iron. Conclusions. The detection of a powerful X-ray flare from HOPS 383 constitutes direct proof that magnetic activity can be present at the earliest formative stages of solar-type stars.

Nicolas Grosso↗

DOE OSTI2016

A HOT AND MASSIVE ACCRETION DISK AROUND THE HIGH-MASS PROTOSTAR IRAS 20126+4104

We present new spectral line observations of the CH{sub 3}CN molecule in the accretion disk around the massive protostar IRAS 20126+4104 with the Submillimeter Array, which, for the first time, measure the disk density, temperature, and rotational velocity with sufficient resolution (0.″37, equivalent to ∼600 au) to assess the gravitational stability of the disk through the Toomre- Q parameter. Our observations resolve the central 2000 au region that shows steeper velocity gradients with increasing upper state energy, indicating an increase in the rotational velocity of the hotter gas nearer the star. Such spin-up motions are characteristics of an accretion flow in a rotationally supported disk. We compare the observed data with synthetic image cubes produced by three-dimensional radiative transfer models describing a thin flared disk in Keplerian motion enveloped within the centrifugal radius of an angular-momentum-conserving accretion flow. Given a luminosity of 1.3 × 10{sup 4} L {sub ⊙}, the optimized model gives a disk mass of 1.5 M {sub ⊙} and a radius of 858 au rotating about a 12.0 M {sub ⊙} protostar with a disk mass accretion rate of 3.9 × 10{sup −5} M {sub ⊙} yr{sup −1}. Our study finds that, in contrast to some theoretical expectations, the disk is hot and stable to fragmentation with Q > 2.8 at all radii which permits a smooth accretion flow. These results put forward the first constraints on gravitational instabilities in massive protostellar disks, which are closely connected to the formation of companion stars and planetary systems by fragmentation.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Protostar l1455 IRS1: a rotating disk connecting to a filamentary network

We conducted IRAM-30 m C{sup 18}O (2–1) and SMA 1.3 mm continuum {sup 12}CO (2–1) and C{sup 18}O (2–1) observations toward the Class 0/I protostar L1455 IRS1 in Perseus. The IRAM-30 m C{sup 18}O results show IRS1 in a dense 0.05 pc core with a mass of 0.54 M {sub ⊙}, connecting to a filamentary structure. Inside the dense core, compact components of 350 au and 1500 au are detected in the SMA 1.3 mm continuum and C{sup 18}O, with a velocity gradient in the latter one perpendicular to a bipolar outflow in {sup 12}CO, likely tracing a rotational motion. We measure a rotational velocity profile ∝r{sup −0.75} that becomes shallower at a turning radius of ∼200 au, which is approximately the radius of the 1.3 mm continuum component. These results hint at the presence of a Keplerian disk with a radius <200 au around L1455 IRS1 with a protostellar mass of about 0.28 M {sub ⊙}. We derive a core rotation that is about one order of magnitude faster than expected. A significant velocity gradient along a filament toward IRS1 indicates that this filament is dynamically important, providing a gas reservoir and possibly responsible for the faster-than-average core rotation. Previous polarimetric observations show a magnetic field aligned with the outflow axis and perpendicular to the associated filament on a 0.1 pc scale, while on the inner 1000 au scale, the field becomes perpendicular to the outflow axis. This change in magnetic field orientations is consistent with our estimated increase in rotational energy from large to small scales that overcomes the magnetic field energy, wrapping the field lines and aligning them with the disk velocity gradient. These results are discussed in the context of the interplay between filament, magnetic field, and gas kinematics from large to small scales. Possible emerging trends are explored with a sample of 8 Class 0/I protostars.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Evolution of mass outflow in protostars

We have surveyed 84 Class 0, Class I, and flat-spectrum protostars in mid-infrared [Si ii], [Fe ii], and [S i] line emission, and 11 of these in far-infrared [O i] emission. We use the results to derive their mass outflow rates, M-dot {sub w}. Thereby we observe a strong correlation of M-dot {sub w} with bolometric luminosity, and with the inferred mass accretion rates of the central objects, M-dot {sub a}, which continues through the Class 0 range the trend observed in Class II young stellar objects. Along this trend from large to small mass flow rates, the different classes of young stellar objects lie in the sequence Class 0–Class I/flat-spectrum–Class II, indicating that the trend is an evolutionary sequence in which M-dot {sub a} and M-dot {sub w} decrease together with increasing age, while maintaining rough proportionality. The survey results include two that are key tests of magnetocentrifugal outflow-acceleration mechanisms: the distribution of the outflow/accretion branching ratio b= M-dot {sub w}/ M-dot {sub a}, and limits on the distribution of outflow speeds. Neither rules out any of the three leading outflow-acceleration, angular-momentum-ejection mechanisms, but they provide some evidence that disk winds and accretion-powered stellar winds (APSWs) operate in many protostars. An upper edge observed in the branching-ratio distribution is consistent with the upper bound of b = 0.6 found in models of APSWs, and a large fraction (31%) of the sample have a branching ratio sufficiently small that only disk winds, launched on scales as large as several au, have been demonstrated to account for them.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

YOUNG STELLAR POPULATIONS IN MYStIX STAR-FORMING REGIONS: CANDIDATE PROTOSTARS

The Massive Young Star-Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star-forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog and Chandra -based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1109 MYStIX Candidate Protostars (MCPs) are found in 14 star-forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few “false positives” from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many “false negatives.” Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be elucidated.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1981

Discovery of a protostar in the Large Magellanic Cloud

A near infrared search of the H II region/molecular cloud complex N159 in the Large Magellanic Cloud has revealed a very red (H-K = 2.1, K-L-prime = 2.7) compact object. The location, brightness, color and 2.1-2.4 micron spectrum of this source suggest that it is very young, and similar to the galactic infrared protostars. This is the first identification of an infrared protostar in an external galaxy. Its discovery provides direct evidence of current star formation in the Large Magellanic Cloud, and suggests that regions of star formation in external galaxies will appear similar to those in the Milky Way.

Gatley, I.↗

NASA NTRS1985

Mass loss rates from protostars and OI(63 micron) shock luminosities

The high-velocity ejection of material from protostars results in a wind shock which may be observable in OI(63 micron) emission. It is shown that for a wide range of conditions, the OI(63 micron) luminosity is proportional to the mass loss rate from the protostar. Application is made to shock OI(63 micron) emission observed around IRc2 in the BN-KL region of Orion.

Hollenbach, D.↗

NASA NTRS1986

The Draco cloud as a matrix of potential protostars

The Draco molecular cloud is inbound at a z distance of a few hundred parsecs, according to previous observations. IRAS Point Source Catalog data for a 36 sq deg area that includes most of the cloud and a comparison area around it are tabulated, illustrated, and discussed. The sources are classified as 56 unidentified, 38 identified extragalactic objects, and 44 identified stars. The unidentified and unresolved 100 micron sources appear to be globule-like clumps that are candidates for producing protostars, although the data cannot demonstrate currently accreting protostars in the globules. An undetermined percent of 100 micron sources may be artifactual, but only a small percent of them may be galaxies because of the adherence to the Draco cloud. Sources detected also at 60 micron or only at 60 micron do not adhere to the cloud and are probably galaxies. Unless artifactual the unidentified and unresolved 100 micron sources may provide considerable new information about the cloud components and therefore about potential star formation in a new class of sites and origins. Six unidentified sources have 12-25 micron stellar spectral distributions, but neither they nor the identified stars have 12-25 micron spectra characteristic of T Tauri stars.

Johnson, Hugh M.↗

NASA NTRS1988

Mass loss from rapidly rotating magnetic protostars

It is proposed that bipolar outflows from young stellar objects originate from a protostar rotating at breakup at its equator because it is being spun up by an adjoining accretion disk. Mass outflow at an appreciable fraction of the infall rate from a surrounding molecular cloud core onto the star and disk can be driven centrifugally if the protostar has a sufficiently strong magnetic field. The expansion of the flow toward the rotational poles may provide a collimation mechanism for focusing an ordinary stellar wind into optical jets.

Shu, Frank H.↗

NASA NTRS1989

Molecule formation in fast neutral winds from protostars

A time-dependent chemical model is used to analyze the processes generating and destroying molecules in very high velocity winds from low-mass protostars. CO and SiO are found to be generated in significant quantities despite the persistence of H in atomic form, consistently with recent protostellar wind detections of CO and H I at velocities in excess of 100 km/sec. A moderate mass-loss rate, in conjunction with a temperature distribution that decreases rather rapidly with distance from the protostar, are the conditions for substantial molecule formation.

Glassgold, A. E.↗

NASA NTRS1989

Numerical models of rotating protostars

The effects of rotation on the internal structure of protostars are examined and the consequences of these effects for evolution are examined using rotating protostar models with various choices of the angular speed of the initial cloud and the mass accretion rate. The temporal order of the onset of convective deuterium burning, attainment of sufficient angular momentum for critical uniform rotation, development of a nearly Keplerian disk through direct infall, and the onset of nonaxisymmetric instability is determined. It is shown that the latter three events always occur in the stated order. Different evolutionary scenarios result depending on when deuterium ignition occurs relative to the other three events.

Durisen, Richard H.↗

NASA NTRS1991

Two protostar candidates in the bright-rimmed dark cloud LDN 1206

The discovery of several near IR objects associated with two IRAS point sources in the LDN 1206 region is reported. IRAS 22272 + 6358A is probably a 'protostar' which is seen only in scattered light at near-IR wavelengths because of heavy obscuration by an almost edge-on circumstellar disk. In contrast, IRAS 22272 + 6358B is directly visible at these wavelengths and is perhaps an object which lies between protostars and T-Tauri stars in its evolution. Both direct and polarimetric K-band images of the region are presented, as well as spectral energy distributions constructed from J, H, K, L, L-prime, and M data and published far-IR and mm data.

Ressler, Michael E.↗

NASA NTRS1992

Methanol ice in the protostar GL 2136

We present ground-based spectra in the 10 and 20 micron atmospheric windows of the deeply embedded protostar GL 2136. These reveal narrow absorption features at 9.7 and 8.9 microns, which we ascribe to the CO-stretch and CH3 rock (respectively) of solid methanol in grain mantles. The peak position of the 9.7 micron band implies that methanol is an important ice mantle component. However, the CH3OH/H2O abundance ratio derived from the observed column densities is only 0.1. This discrepancy suggests that the solid methanol and water ice are located in independent grain components. These independent components may reflect chemical differentiation during grain mantle formation and/or partial outgassing close to the protostar.

Skinner, C. J.↗

NASA NTRS1992

Circumprotostellar environments. I - Molecular outflows from protostar candidates in Taurus

We report on the search for molecular outflows from a complete, flux-limited, IRAS-selected sample of cold, low-mass protostar candidates located in the Taurus cloud complex. We find that 18 of the 24 sources have outflows associated with them, only four of which have been previously reported, implying that these sources are predominantly protostars in an early stage of evolution. We argue that at least a few of the outflows are very small in extent, indicating that their dynamical ages are less than a few thousand years.

Moriarty-Schieven, G. H.↗

NASA NTRS2001

High Resolution 4.7 Micron Keck/NIRSPEC Spectra of Protostars: Ices and Infalling Gas in the Disk of L1489 IRS - 1

We explore the infrared M band (4.7 micron) spectrum of the class I protostar L1489 IRS in the Taurus Molecular Cloud. This is the highest resolution wide coverage spectrum at this wavelength of a low mass protostar observed to date (R =25,000; (Delta)v =12 km s(exp -1). A large number of narrow absorption lines of gas phase (12)CO, (13)CO, and C(sup 18)O are detected, as well as a prominent band of solid (12)CO. The gas phase (12)CO lines have red shifted absorption wings (up to 100 km s(exp -1)), which likely originate from warm disk material falling toward the central object. Both the isotopes and the extent of the (12)CO line wings are successfully fitted with a contracting disk model of this evolutionary transitional object. This shows that the inward motions seen in millimeter wave emission lines continue to within approx. 0.1 AU from the star. The amount of high velocity infalling gas is however overestimated by this model, suggesting that only part of the disk is infalling, e.g. a hot surface layer or hot gas in magnetic field tubes. The colder parts of the disk are traced by the prominent CO ice band. The band profile results from CO in 'polar' ices (CO mixed with H2O), and CO in 'apolar' ices. At the high spectral resolution, the 'apolar' component is, for the first time, resolved into two distinct components, likely due to pure CO and CO mixed with CO2, O2 and/or N2. The ices have probably experienced thermal processing in the upper disk layer traced by our pencil absorption beam: much of the volatile 'apolar' ices has evaporated, the depletion factor of CO onto grains is remarkably low (approx. 7%), and the CO2 traced in the CO band profile was possibly formed energetically. This study shows that high spectral resolution 4.7 micron observations provide important and unique information on the dynamics and structure of protostellar disks and the origin and evolution of ices in these disks.

Boogert, A. C. A.↗

NASA NTRS2011

Molecular Anions in Protostars, Prestellar Cores and Dark Clouds

From our recent survey work using the Green Bank Telescope, microwave emission lines from the hydrocarbon anion C6H(-) and its parent neutral C6H have been detected in six new sources. Using HC3N = 10(exp -9) emission maps, we targeted the most carbon-chain-rich sources for our anion survey, which included the low-mass Class 0 protostar L1251A-IRS3, the prestellar cores L1389-SMM1 and L1512, and the interstellar clouds Ll172A, TMC-1C and L1495B. Derived [C6H(-)]/[C6H] anion-to-neutral ratios are approximately 1-10. The greatest C6H(-) column densities are found in the quiescent clouds TMC-1C and L1495B, but the anion-to-neutral ratios are greatest in the prestellar cores and protostars. These results are interpreted in terms of the physical and chemical properties of the sources, and the implications for molecular cloud chemistry are discussed.

Cordiner, Martin↗

NASA NTRS2005

Proceedings of Protostars and Planets V

Oral presentation sessions in this conference include: Clouds and cores; Star formation and protostars; Binaries and multiples; Newborn massive stars; jets and outflows; Clusters and associations; T Tauri stars and disks; Brown dwarfs; Planet formation and evolution; Extrasolar planets; Dust and protoplanetary disks; Early solar system and Astrobiology. Poster presentations included: Clouds and Cores. Collapse and Protostars, Binaries and Multiples, Clusters, Associations, and the IMF, Jets and Outflows, T Tauri Stars and Other Young Stars, Disks and Disk Accretion, Brown Dwarfs, Herbig Ae/Be Stars and Massive Stars, Solar System Objects, Planet Formation, Extrasolar Planets and Planet Detection, Properties of Protoplanetary Disks, Migration and Planetary Orbits and Meteoritics and Astrobiology

Source record↗

NASA NTRS2012

Observations of Carbon Chain Chemistry in the Envelopes of Low-Mass Protostars

Observational results are reported from our surveys in the Northern Hemisphere (using the Onsala 20 m telescope) and the Southern Hemisphere (using the Mopra 22 m telescope) to search for 3 mm emission lines from carbon-chain-bearing species and other complex molecules in the envelopes of low-mass protostars. Based on a sample of approximately 60 sources, we find that carbon-chain-bearing species including HC3N (and C4H) are highly abundant in the vicinity of more than half of the observed protostars. The origin and evolution of these species, including their likely incorporation into ices in protoplanetary disks will be discussed

Cordiner, M.↗