28 research outputs found
Identifying the Chemical Impact and the Mechanism of an Accretion Outburst on a Class 0 Protostar
Past and present observations of luminosity bursts in various young protostars provide increasing evidence that episodic accretion is a common phenomenon in protostellar evolution. Studying these outbursting systems can help reveal the dynamics of mass accretion in protostars and constrain the properties and nature of protostellar disks. I present a study of the youngest known outbursting protostar, HOPS 383, a Class 0 protostar in the Orion molecular cloud using observations from the Submillimeter Array (SMA), the Atacama Large Millimeter/submillimeter Array (ALMA), and the Very Large Array (VLA). First, I use the SMA to study the effect of the outburst on the chemistry of the disk and the envelope around HOPS 383. The SMA observations show peaked HCO+ and H13CO+ and reduced N2H+ at the protostar position, consistent with chemical models of outbursting YSOs where the evaporating CO increases HCO+ and decreases N2H+. Second, I present dust continuum observed with the ALMA at 0.87 mm and the VLA at 9 mm to constrain the disk properties and understand its role in protostellar evolution. Both the continuum show a well-resolved disk orthogonal to the outflow. The outflow is traced by 12CO, evident both in the SMA and the ALMA data, suggesting that HOPS 383 is quite young. Assuming isothermal and optically thin dust emission, I estimate the current disk mass between 0.043 Msun and 0.15 Msun. To assess of gravitational instability (GI) as the cause of the outburst, I calculate Toomre's Q ~1.14 and ~0.87 pre-outburst, using the ALMA and the VLA derived disk masses, respectively. Finally, modeling the resolved continuum from the ALMA and the VLA using 3D radiative transfer code gives disk masses of 0.1 Msun and 0.065 Msun for the ALMA only models and disk masses of 0.25 Msun and 0.21 Msun for the ALMA+VLA models. The disk temperature and surface density profiles from the modeling suggest that Toomre's Q < 1 for most cases before the outburst, suggesting that GI possibly drove the outburst in HOPS 383 and is a viable mechanism to explain outbursts at an early age if the disk is sufficiently massive
Constraining the Chemical Signatures and the Outburst Mechanism of the Class 0 Protostar HOPS 383
We present observations toward HOPS 383, the first known outbursting Class 0
protostar located within the Orion molecular cloud using ALMA, VLA, and SMA.
The SMA observations reveal envelope scale continuum and molecular line
emission surrounding HOPS 383 at 0.85 mm, 1.1 mm, and 1.3 mm. The images show
that HCO and HCO peaks on or near the continuum, while
NH is reduced at the same position. This reflects the underlying
chemistry where CO evaporating close to the protostar destroys NH while
forming HCO. We also observe the molecular outflow traced by CO () and (). A disk is resolved in the ALMA
0.87 mm dust continuum, orthogonal to the outflow direction, with an apparent
radius of 62 AU. Radiative transfer modeling of the continuum gives disk
masses of 0.02 M when fit to the ALMA visibilities. The models
including VLA 8 mm data indicate that the disk mass could be up to a factor of
10 larger due to lower dust opacity at longer wavelengths. The disk temperature
and surface density profiles from the modeling, and an assumed protostar mass
of 0.5 M suggest that the Toomre parameter before the
outburst, making gravitational instability a viable mechanism to explain
outbursts at an early age if the disk is sufficiently massive.Comment: Accepted by Ap
Constraining the Chemical Signatures and the Outburst Mechanism of the Class 0 Protostar HOPS 383
Early Planet Formation in Embedded Disks (eDisk) X: Compact Disks, Extended Infall, and a Fossil Outburst in the Class I Oph IRS43 Binary
We present the first results from the Early Planet Formation in Embedded
Disks (eDisk) ALMA Large Program toward Oph IRS43, a binary system of solar
mass protostars. The 1.3 mm dust continuum observations resolve a compact disk,
~6au radius, around the northern component and show that the disk around the
southern component is even smaller, <~3 au. CO, 13CO, and C18O maps reveal a
large cavity in a low mass envelope that shows kinematic signatures of rotation
and infall extending out to ~ 2000au. An expanding CO bubble centered on the
extrapolated location of the source ~130 years ago suggests a recent outburst.
Despite the small size of the disks, the overall picture is of a remarkably
large and dynamically active region.Comment: Paper 10 of the ALMA eDisk Large Program. Accepted for publication in
Ap
Early Planet Formation in Embedded Disks (eDisk). VIII. A Small Protostellar Disk around the Extremely Low-Mass and Young Class 0 Protostar, IRAS 15398-3359
Protostellar disks are a ubiquitous part of the star formation process and
the future sites of planet formation. As part of the Early Planet Formation in
Embedded Disks (eDisk) large program, we present high-angular resolution dust
continuum (mas) and molecular line (mas) observations of
the Class 0 protostar, IRAS 15398-3359. The dust continuum is small, compact,
and centrally peaked, while more extended dust structures are found in the
outflow directions. We perform a 2D Gaussian fitting to find the deconvolved
size and radius of the dust disk to be
and , respectively. We estimate the gas+dust disk mass
assuming optically thin continuum emission to be ,
indicating a very low-mass disk. The CO isotopologues trace components of the
outflows and inner envelope, while SO traces a compact, rotating disk-like
component. Using several rotation curve fittings on the PV diagram of the SO
emission, the lower limits of the protostellar mass and gas disk radius are
and from our Modified 2 single power-law
fitting. A conservative upper limit of the protostellar mass is inferred to be
. The protostellar mass-accretion rate and the specific angular
momentum at the protostellar disk edge are found to be between
and
, respectively, with an age
estimated between yr. At this young age with no clear
substructures in the disk, planet formation would likely not yet have started.
This study highlights the importance of high-resolution observations and
systematic fitting procedures when deriving dynamical properties of deeply
embedded Class 0 protostars.Comment: 28 pages, 16 figures. Accepted for publication in ApJ as one of the
first-look papers of the eDisk ALMA Large Progra
Early Planet Formation in Embedded Disks (eDisk) VI: Kinematic Structures around the Very Low Mass Protostar IRAS 16253-2429
Precise estimates of protostellar masses are crucial to characterize the
formation of stars of low masses down to brown-dwarfs (BDs; M* < 0.08 Msun).
The most accurate estimation of protostellar mass uses the Keplerian rotation
in the circumstellar disk around the protostar. To apply the Keplerian rotation
method to a protostar at the low-mass end, we have observed the Class 0
protostar IRAS 16253-2429 using the Atacama Large Millimeter/submillimeter
Array (ALMA) in the 1.3 mm continuum at an angular resolution of 0.07" (10 au),
and in the 12CO, C18O, 13CO (J=2-1), and SO (J_N = 6_5-5_4) molecular lines, as
part of the ALMA Large Program Early Planet Formation in Embedded Disks
(eDisk). The continuum emission traces a non-axisymmetric, disk-like structure
perpendicular to the associated 12CO outflow. The position-velocity (PV)
diagrams in the C18O and 13CO lines can be interpreted as infalling and
rotating motions. In contrast, the PV diagram along the major axis of the
disk-like structure in the 12CO line allows us to identify Keplerian rotation.
The central stellar mass and the disk radius are estimated to be ~0.12-0.17
Msun and ~13-19 au, respectively. The SO line suggests the existence of an
accretion shock at a ring (r~28 au) surrounding the disk and a streamer from
the eastern side of the envelope. IRAS 16253-2429 is not a proto-BD but has a
central stellar mass close to the BD mass regime, and our results provide a
typical picture of such very low-mass protostars.Comment: 41 pages, 14 figure
Early Planet Formation in Embedded Disks (eDisk) V: Possible Annular Substructure in a Circumstellar Disk in the Ced110 IRS4 System
We have observed the Class 0/I protostellar system Ced110 IRS4 at an angular
resolution of (10 au) as a part of the ALMA large program; Early
Planet Formation in the Embedded Disks (eDisk). The 1.3 mm dust continuum
emission reveals that Ced110 IRS4 is a binary system with a projected
separation of 250 au. The continuum emissions associated with the main
source and its companion, named Ced110 IRS4A and IRS4B respectively, exhibit
disk-like shapes and likely arise from dust disks around the protostars. The
continuum emission of Ced110 IRS4A has a radius of 110 au (),
and shows bumps along its major axis with an asymmetry. The bumps can be
interpreted as an shallow, ring-like structure at a radius of 40 au
() in the continuum emission, as demonstrated from two-dimensional
intensity distribution models. A rotation curve analysis on the CO and
CO -1 lines reveals the presence of a Keplerian disk within a
radius of 120 au around Ced110 IRS4A, which supports the interpretation that
the dust continuum emission arises from a disk. The ring-like structure in the
dust continuum emission might indicate a possible, annular substructure in the
surface density of the embedded disk, although the possibility that it is an
apparent structure due to the optically thick continuum emission cannot be
ruled out.Comment: 32 pages, 23 figures. Accepted for publication in ApJ as one of the
first-look papers of the eDisk ALMA Large Progra
Early Planet Formation in Embedded Disks (eDisk) XII: Accretion streamers, protoplanetary disk, and outflow in the Class I source Oph IRS63
We present ALMA observations of the Class I source Oph IRS63 in the context
of the Early Planet Formation in Embedded Disks (eDisk) large program. Our ALMA
observations of Oph IRS63 show a myriad of protostellar features, such as a
shell-like bipolar outflow (in CO), an extended rotating envelope
structure (in CO), a streamer connecting the envelope to the disk (in
CO), and several small-scale spiral structures seen towards the edge of
the dust continuum (in SO). By analyzing the velocity pattern of CO and
CO, we measure a protostellar mass of ~ and confirm the presence of a disk rotating at almost Keplerian
velocity that extends up to au. These calculations also show that the
gaseous disk is about four times larger than the dust disk, which could
indicate dust evolution and radial drift. Furthermore, we model the CO
streamer and SO spiral structures as features originating from an infalling
rotating structure that continuously feeds the young protostellar disk. We
compute an envelope-to-disk mass infall rate of ~ and compare it to the disk-to-star mass accretion rate of ~, from which we infer that the protostellar
disk is in a mass build-up phase. At the current mass infall rate, we speculate
that soon the disk will become too massive to be gravitationally stable.Comment: 26 pages and 17 figure
Early Planet Formation in Embedded Disks (eDisk). IV. The Ringed and Warped Structure of the Disk around the Class I Protostar L1489 IRS
Constraining the physical and chemical structure of young embedded disks is
crucial to understanding the earliest stages of planet formation. As part of
the Early Planet Formation in Embedded Disks Atacama Large
Millimeter/submillimeter Array Large Program, we present high spatial
resolution (0.\!\!^{\prime\prime}1 or 15 au) observations of the
1.3 mm continuum and CO 2-1, CO 2-1, and SO
- molecular lines toward the disk around the Class I protostar L1489
IRS. The continuum emission shows a ring-like structure at 56 au from the
central protostar and a tenuous, optically thin emission extending beyond
300 au. The CO emission traces the warm disk surface, while the
CO emission originates from near the disk midplane. The coincidence of
the radial emission peak of CO with the dust ring may indicate a
gap-ring structure in the gaseous disk as well. The SO emission shows a highly
complex distribution, including a compact, prominent component at 30
au, which is likely to originate from thermally sublimated SO molecules. The
compact SO emission also shows a velocity gradient along a slightly
() tilted direction with respect to the major axis of the dust
disk, which we interpret as an inner warped disk in addition to the warp around
200 au suggested by previous work. These warped structures may be formed
by a planet or companion with an inclined orbit, or by a gradual change in the
angular momentum axis during gas infall.Comment: 24 pages, 12 figures. Accepted for publication in The Astrophysical
Journal as one of the first-look papers of the eDisk ALMA Large Progra