146 research outputs found
A Disk-based Dynamical Mass Estimate for the Young Binary AK Sco
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 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, , a new dynamical measurement
that is independent of stellar evolutionary models. Assuming the disk and
binary are co-planar within 2{\deg}, 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-main
sequence model grids. These models predict stellar masses that are marginally
consistent with our dynamical measurement (at ), but are
systematically high (by 10%). These same models consistently predict an
age of 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-main sequence 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.Comment: Accepted to The Astrophysical Journa
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 = 2ā1 line emission, we infer the mass of the central binary, M* = 2.49 Ā± 0.10 Mā, a new dynamical measurement that is independent of stellar evolutionary models. Assuming the disk and binary are co-planar within ā¼2Ā°, 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 HertzsprungāRussell diagram, using several common pre-MS model grids. These models predict stellar masses that are marginally consistent with our dynamical measurement (at ā¼2Ļ), but are systematically high (by ā¼10%). These same models consistently predict an age of 18 Ā± 1 Myr for AK Sco, in line with its membership in the Upper CentaurusāLupus 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
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+0.46Ā Mā. 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 Ā± 0.26 Mā and that the disk and binary orbital planes are aligned within 3Ā° (at 3Ļ 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 āweighedā 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 degree of alignment between circumbinary disks and their binary hosts
Funding: I.C. was supported by NASA through the NASA Hubble Fellowship grant HST-HF2-51405.001-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.All four circumbinary (CB) protoplanetary disks orbiting short-period (P < 20 days) double-lined spectroscopic binaries (SB2s)āa group that includes UZ Tau E, for which we present new Atacama Large Millimeter/Submillimeter Array dataāexhibit sky-plane inclinations idisk that match, to within a few degrees, the sky-plane inclinations iā of their stellar hosts. Although for these systems the true mutual inclinations Īø between disk and binary cannot be directly measured because relative nodal angles are unknown, the near coincidence of i disk and iā suggests that Īø 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 Īø < 3.Ā°0. 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.Publisher PDFPeer reviewe
The Architecture of the GW Ori Young Triple Star System and Its Disk: Dynamical Masses, Mutual Inclinations, and Recurrent Eclipses
We present spatially and spectrally resolved Atacama Large
Millimeter/submillimeter Array (ALMA) observations of gas and dust orbiting the
pre-main sequence hierarchical triple star system GW Ori. A forward-modeling of
the CO and CO =2-1 transitions permits a measurement of
the total stellar mass in this system, , and the
circum-triple disk inclination, . Optical spectra spanning
a 35 year period were used to derive new radial velocities and, coupled with a
spectroscopic disentangling technique, revealed that the A and B components of
GW Ori form a double-lined spectroscopic binary with a day
period; a tertiary companion orbits that inner pair with a day
period. Combining the results from the ALMA data and the optical spectra with
three epochs of astrometry in the literature, we constrain the individual
stellar masses in the system (,
, ) and
find strong evidence that at least one (and likely both) stellar orbital planes
are misaligned with the disk plane by as much as . A -band light
curve spanning 30 years reveals several new 30 day eclipse events
0.1-0.7~mag in depth and a 0.2 mag sinusoidal oscillation that is clearly
phased with the AB-C orbital period. Taken together, these features suggest
that the A-B pair may be partially obscured by material in the inner disk as
the pair approaches apoastron in the hierarchical orbit. Lastly, we conclude
that stellar evolutionary models are consistent with our measurements of the
masses and basic photospheric properties if the GW Ori system is 1 Myr
old.Comment: 26 pages, 15 figures, accepted to Ap
Ultra-Luminous Supernovae as a New Probe of the Interstellar Medium in Distant Galaxies
We present the Pan-STARRS1 discovery and light curves, and follow-up MMT and
Gemini spectroscopy of an ultra-luminous supernova (ULSN; dubbed PS1-11bam) at
a redshift of z=1.566 with a peak brightness of M_UV=-22.3 mag. PS1-11bam is
one of the highest redshift spectroscopically-confirmed SNe known to date. The
spectrum is characterized by broad absorption features typical of previous
ULSNe (e.g., CII, SiIII), and by strong and narrow MgII and FeII absorption
lines from the interstellar medium (ISM) of the host galaxy, confirmed by an
[OII]3727 emission line at the same redshift. The equivalent widths of the
FeII2600 and MgII2803 lines are in the top quartile of the quasar intervening
absorption system distribution, but are weaker than those of gamma-ray burst
intrinsic absorbers (i.e., GRB host galaxies). We also detect the host galaxy
in pre-explosion Pan-STARRS1 data and find that its UV spectral energy
distribution is best fit with a young stellar population age of tau~15-45 Myr
and a stellar mass of M \sim (1.1-2.6)x10^9 M_sun (for Z=0.05-1 Z_sun). The
star formation rate inferred from the UV continuum and [OII]3727 emission line
is ~10 M_sun/yr, higher than in any previous ULSN host. PS1-11bam provides the
first direct demonstration that ULSNe can serve as probes of the interstellar
medium in distant galaxies. At the present, the depth and red sensitivity of
PS1 are uniquely suited to finding such events at cosmologically interesting
redshifts (z~1-2); the future combination of LSST and 30-m class telescopes
promises to extend this technique to z~4.Comment: Submitted to ApJL; 9 pages; 4 figures; 1 tabl
PS1-10afx at z=1.388: Pan-STARRS1 Discovery of a New Type of Superluminous Supernova
We present the Pan-STARRS1 discovery of PS1-10afx, a unique
hydrogen-deficient superluminous supernova (SLSN) at z=1.388. The light curve
peaked at z_P1=21.7 mag, making PS1-10afx comparable to the most luminous known
SNe, with M_u = -22.3 mag. Our extensive optical and NIR observations indicate
that the bolometric light curve of PS1-10afx rose on the unusually fast
timescale of ~12 d to the extraordinary peak luminosity of 4.1e44 erg/s (M_bol
= -22.8 mag) and subsequently faded rapidly. Equally important, the SED is
unusually red for a SLSN, with a color temperature of 6800 K near maximum
light, in contrast to previous H-poor SLSNe, which are bright in the UV. The
spectra more closely resemble those of a normal SN Ic than any known SLSN, with
a photospheric velocity of 11,000 km/s and evidence for line blanketing in the
rest-frame UV. Despite the fast rise, these parameters imply a very large
emitting radius (>5e15 cm). We demonstrate that no existing theoretical model
can satisfactorily explain this combination of properties: (i) a nickel-powered
light curve cannot match the combination of high peak luminosity with the fast
timescale; (ii) models powered by the spindown energy of a rapidly-rotating
magnetar predict significantly hotter and faster ejecta; and (iii) models
invoking shock breakout through a dense circumstellar medium cannot explain the
observed spectra or color evolution. The host galaxy is well detected in
pre-explosion imaging with a luminosity near L*, a star formation rate of 15
M_sun/yr, and is fairly massive (2e10 M_sun), with a stellar population age of
1e8 yr, also in contrast to the dwarf hosts of known H-poor SLSNe. PS1-10afx is
distinct from known examples of SLSNe in its spectra, colors, light-curve
shape, and host galaxy properties, suggesting that it resulted from a different
channel than other hydrogen-poor SLSNe.Comment: 17 pages, 12 figures, accepted to ApJ, minor revisions, including
expanded discussion of lensing hypothesi
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