33 research outputs found
Fe I and Fe II Abundances of Solar-Type Dwarfs in the Pleiades Open Cluster
We have derived Fe abundances of 16 solar-type Pleiades dwarfs by means of an
equivalent width analysis of Fe I and Fe II lines in high-resolution spectra
obtained with the Hobby - Eberly Telescope and High Resolution Spectrograph.
Abundances derived from Fe II lines are larger than those derived from Fe I
lines (herein referred to as over-ionization) for stars with Teff < 5400 K, and
the discrepancy (deltaFe = [Fe II/H] - [Fe I/H]) increases dramatically with
decreasing Teff, reaching over 0.8 dex for the coolest stars of our sample. The
Pleiades joins the open clusters M 34, the Hyades, IC 2602, and IC 2391, and
the Ursa Major moving group, demonstrating ostensible over-ionization trends.
The Pleiades deltaFe abundances are correlated with Ca II infrared triplet and
Halpha chromospheric emission indicators and relative differences therein.
Oxygen abundances of our Pleiades sample derived from the high-excitation O I
triplet have been previously shown to increase with decreasing Teff, and a
comparison with the deltaFe abundances suggests that the over-excitation
(larger abundances derived from high excitation lines relative to low
excitation lines) and over-ionization effects that have been observed in cool
open cluster and disk field main sequence (MS) dwarfs share a common origin.
Star-to-star Fe I abundances have low internal scatter, but the abundances of
stars with Teff < 5400 K are systematically higher compared to the warmer
stars. The cool star [Fe I/H] abundances cannot be connected directly to
over-excitation effects, but similarities with the deltaFe and O I triplet
trends suggest the abundances are dubious. Using the [Fe I/H] abundances of
five stars with Teff > 5400 K, we derive a mean Pleiades cluster metallicity of
[Fe/H] = +0.01 +/- 0.02.Comment: 32 pages, 7 figures, 7 tables; accepted by PAS
Assessing molecular outflows and turbulence in the protostellar cluster Serpens South
Molecular outflows driven by protostellar cluster members likely impact their
surroundings and contribute to turbulence, affecting subsequent star formation.
The very young Serpens South cluster consists of a particularly high density
and fraction of protostars, yielding a relevant case study for protostellar
outflows and their impact on the cluster environment. We combined CO
observations of this region using the Combined Array for Research in
Millimeter-wave Astronomy (CARMA) and the Institut de Radioastronomie
Millim\'{e}trique (IRAM) 30 m single dish telescope. The combined map allows us
to probe CO outflows within the central, most active region at size scales of
0.01 pc to 0.8 pc. We account for effects of line opacity and excitation
temperature variations by incorporating CO and CO data for the
and transitions (using Atacama Pathfinder Experiment and
Caltech Submillimeter Observatory observations for the higher CO transitions),
and we calculate mass, momentum, and energy of the molecular outflows in this
region. The outflow mass loss rate, force, and luminosity, compared with
diagnostics of turbulence and gravity, suggest that outflows drive a sufficient
amount of energy to sustain turbulence, but not enough energy to substantially
counter the gravitational potential energy and disrupt the clump. Further, we
compare Serpens South with the slightly more evolved cluster NGC 1333, and we
propose an empirical scenario for outflow-cluster interaction at different
evolutionary stages.Comment: 26 pages, 15 figures, accepted for publication in the Astrophysical
Journa
The Structure of Dense Gas in Perseus and Serpens: CLASSy Results
We present results of a dendrogram analysis of N2H+ J=1-0 data cubes from the CARMA Large Area Star-formation Survey (CLASSy). Dendrogram tree structures are characterized by their morphology and kinematics relative to one another, and provide a useful mechanism for analyzing the hierarchy of molecular regions from core-to-cloud spatial scales. Our CARMA data, with 7" spatial and 0.15 km/sec velocity resolution, yield the following results: (1) trees are more hierarchical in regions of high star formation activity; (2) in all regions, the leaf and branch morphology is widely varying and mostly not circularly symmetric; (3) there is evidence for multiple velocity components along a line of sight in only a small fraction of the mapped areas. We compare the identified N2H+ dendrogram tree structures to Herschel maps of dust emission and to Spitzeridentified young stellar object distributions to compare the dense gas distribution to the current star formation activity.Fil: Mundy, Lee G.. University of Maryland; Estados UnidosFil: Storm, Shaye. University of Maryland; Estados UnidosFil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones CientÃficas. Instituto Argentino de RadioastronomÃa. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto Argentino de RadioastronomÃa; ArgentinaFil: Lee, Katherine. University of Illinois; Estados UnidosFil: Looney, Leslie. University of Illinois; Estados UnidosFil: Teuben, Peter J.. University of Maryland; Estados UnidosFil: Rosolowsky, Erik. University of Alberta; CanadáFil: Shirley, Yancy L.. University of Arizona; Estados UnidosFil: Arce, Hector G.. Yale University; Estados UnidosFil: Plunkett, Adele. Yale University; Estados UnidosFil: Isella, Andrea. Caltech; Estados Unidos223th meeting of the American Astronomical SocietyWashingtonEstados UnidosAmerican Astronomical Societ
Kinematics and Temperature Structures of Filaments in Serpens Main and Serpens South
We present a study of filaments in Serpens Main and Serpens South cluster regions based on N2H+(1-0) observations from the CARMA Large Area Star-formation Survey (CLASSy) and dust continuum images from the Herschel Space Observatory. Serpens Main and Serpens South are active star formation regions with prominent filamentary structures; however, the role of the filaments in the cluster formation is unclear. This study of filament structure and kinematics with high-angular resolution data (7 arcsecs), particularly in revealing possible infall signatures, provides physical insight to this question. Using the Herschel data, we estimate the temperature in and along filaments for comparison with their gas kinematics, spatial distribution, and N2H+(1-0) emission, to better understand their role in current star formation activities.Fil: Lee, Katherine. University of Maryland; Estados UnidosFil: Mundy, Lee G.. University of Maryland; Estados UnidosFil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones CientÃficas. Instituto Argentino de RadioastronomÃa. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto Argentino de RadioastronomÃa; ArgentinaFil: Storm, Shaye. University of Maryland; Estados UnidosFil: Looney, Leslie. University of Illinois at Urbana- Champaign; Estados UnidosFil: Segura Cox, Dominique. University of Maryland; Estados UnidosFil: Teuben, Peter J.. University of Maryland; Estados UnidosFil: Rosolowsky, Erik. University of Alberta; CanadáFil: Arce, Hector G.. Yale University; Estados UnidosFil: Shirley, Yancy L.. University of Arizona; Estados UnidosFil: Plunkett, Adele. Yale University; Estados UnidosFil: Isella, Andrea. Caltech; Estados UnidosFil: Tobin, John J.. National Radio Astronomy Observatory; Estados Unidos223th meeting of the American Astronomical SocietyWashingtonEstados UnidosAmerican Astronomical Societ
The VLA Nascent Disk And Multiplicity (VANDAM) Survey of Perseus Protostars. Resolving the Sub-Arcsecond Binary System in NGC 1333 IRAS2A
We are conducting a Jansky VLA Ka-band (8 mm and 1 cm) and C-band (4 cm and
6.4 cm) survey of all known protostars in the Perseus Molecular Cloud,
providing resolution down to 0.06'' and 0.35" in Ka-band and
C-band, respectively. Here we present first results from this survey that
enable us to examine the source NGC 1333 IRAS2A in unprecedented detail and
resolve it into a proto-binary system separated by 0.621"0.006" (143
AU) at 8 mm, 1 cm, and 4 cm. These 2 sources (IRAS2A VLA1 and VLA2) are likely
driving the two orthogonal outflows known to originate from IRAS2A. The
brighter source IRAS2A VLA1 is extended perpendicular to its outflow in the VLA
data, with a deconvolved size of 0.055" (13 AU), possibly tracing a
protostellar disk. The recently reported candidate companions (IRAS2A MM2 and
MM3) are not detected in either our VLA data, CARMA 1.3 mm data, or SMA 850
m data. SMA CO (), CARMA CO (), and
lower resolution CARMA CO () observations are used to examine
the outflow origins and the nature of the candidate companions to IRAS2A VLA1.
The CO () and () data show that IRAS2A MM2 is
coincident with a bright CO emission spot in the east-west outflow, and IRAS2A
MM3 is within the north-south outflow. In contrast, IRAS2A VLA2 lies at the
east-west outflow symmetry point. We propose that IRAS2A VLA2 is the driving
source of the East-West outflow and a true companion to IRAS2A VLA1, whereas
IRAS2A MM2 and MM3 may not be protostellar.Comment: Accepted to ApJ, 27 pages, 6 Figures, 2 Table
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
Episodic molecular outflow in the very young protostellar cluster Serpens South
The loss of mass from protostars, in the form of a jet or outflow, is a necessary counterpart to protostellar mass accretion. Outflow ejection events probably vary in their velocity and/or in the rate of mass loss. Such `episodic´ ejection events have been observed during the Class 0 protostellar phase (the early accretion stage), and continue during the subsequent class I phase that marks the first one million years of star formation. Previously observed episodic-ejection sources were relatively isolated; however, the most common sites of star formation are clusters. Outflows link protostars with their environment and provide a viable source of turbulence that is necessary for regulating star formation in clusters, but it is not known how an accretion-driven jet or outflow in a clustered environment manifests itself in its earliest stage. This early stage is important in establishing the initial conditions for momentum and energy transfer to the environment as the protostar and cluster evolve. Here we report that an outflow from a very young class 0 protostar, at the hub of the very active and filamentary Serpens South protostellar cluster, shows unambiguous episodic events. The 12CO (J=2-1) emission from the protostar reveals 22 distinct features of outflow ejecta, the most recent having the highest velocity. The outflow forms bipolar lobes --- one of the first detectable signs of star formation --- which originate from the peak of 1-mm continuum emission. Emission from the surrounding C18O envelope shows kinematics consistent with rotation and an infall of material onto the protostar. The data suggest that episodic accretion-driven outflow begins in the earliest phase of protostellar evolution, and that the outflow remains intact in a very clustered environment, probably providing efficient momentum transfer for driving turbulence. Fil: Plunkett, Adele L. . Yale University. Astronomy Department.; Estados UnidosFil: Arce, Héctor G.. Yale University. Astronomy Department.; Estados UnidosFil: Mardones, Diego . Universidad de Chile. Departamento de AstronomÃa; ChileFil: van Dokkum, Pieter . Yale University. Astronomy Department.; Estados UnidosFil: Dunham, Michael M. . Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: Fernandez Lopez, Manuel. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico La Plata. Instituto Argentino de Radioastronomia (i); ArgentinaFil: Gallardo, José. Joint ALMA Observatory; ChileFil: Cordero, Stuartt A. . Joint ALMA Observatory; Chil
CARMA Large Area Star Formation Survey: Structure and Kinematics of Dense Gas in Serpens Main
We present observations of N2H+(1-0), HCO+(1-0), and HCN(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 arcsecs. 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 N2H+(1-0) to study the gas
structures; the SE subcluster has a higher degree of hierarchy than the NW
subcluster. Combining the dendrogram and 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.Comment: Accepted to ApJ. 38 pages, 16 figures, 5 table
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) 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