996 research outputs found
Protoplanetary Disk Mass Distribution in Young Binaries
We present millimeter-wave continuum images of four wide (separations 210-800
AU) young stellar binary systems in the Taurus-Auriga star-forming region. For
all four sources, the resolution of our observations is sufficient to determine
the mm emission from each of the components. In all four systems, the primary
star's disk has stronger millimeter emission than the secondary and in three of
the four, the secondary is undetected; this is consistent with predictions of
recent models of binary formation by fragmentation. The primaries'
circumstellar disk masses inferred from these observations are comparable to
those found for young single stars, confirming that the presence of a wide
binary companion does not prevent the formation of a protoplanetary disk. Some
of the secondaries show signatures of accretion (H-alpha emission and K - L
excesses), yet their mm fluxes suggest that very little disk mass is present.Comment: Accepted by ApJ, to appear Feb. 2003; 9 pages, 5 postscript figures,
uses aastex, emulateapj5, and apjfonts style files. Also available at
http://astro.swarthmore.edu/~jensen/publications.htm
A Connection between Submillimeter Continuum Flux and Separation in Young Binaries
We have made sensitive 800-micron continuum observations of low-mass,
pre-main sequence (PMS) binary stars with projected separations less than 25 AU
in Taurus-Auriga to study disks in the young binary environment. We did not
detect any of the observed binaries, with typical 3-sigma upper limits of about
30 mJy. Combining our observations with previous 1300-micron observations of
PMS Taurus binaries by Beckwith et al. (1990) and others, we find that the
submillimeter fluxes from binaries with projected separations between 1 AU and
50 AU are significantly lower than fluxes from binaries with projected
separations > 50 AU. The submillimeter fluxes from the wider binaries are
consistent with those of PMS single stars. This may indicate lower disk surface
densities and masses in the close binaries. Alternatively, dynamical clearing
of gaps by close binaries is marginally sufficient to lower their submillimeter
fluxes to the observed levels, even without reduction of surface densities
elsewhere in the disks.Comment: 12 pages, uuencoded compressed postscript with figures; Wisconsin
Astrophysics 526; to appear in ApJ Letter
Young Binary Stars and Associated Disks
The typical product of the star formation process is a binary star. Binaries
have provided the first dynamical measures of the masses of pre-main-sequence
(PMS) stars, providing support for the calibrations of PMS evolutionary tracks.
Surprisingly, in some star-forming regions PMS binary frequencies are higher
than among main-sequence solar-type stars. The difference in PMS and
main-sequence binary frequencies is apparently not an evolutionary effect;
recent attention has focussed on correlations between binary frequency and
stellar density or cloud temperatures. Accretion disks are common among young
binary stars. Binaries with separations between 1 AU and 100 AU have
substantially less submillimeter emission than closer or wider binaries,
suggesting that they have truncated their disks. Evidence of dynamical clearing
has been seen in several binaries. Remarkably, PMS binaries of all separations
show evidence of circumstellar disks and continued accretion. This suggests
that the circumstellar disks are replenished from circumbinary disks or
envelopes. The frequent presence of disks suggests that planet formation can
occur in binary environments, and formation of planets in wide binaries is
already established by their discovery. Circumbinary disk masses around very
short period binaries are ample to form planetary systems such as our own. The
nature of planetary systems among the most common binaries, with separations
between 10 AU and 100 AU, is less clear given the observed reduction in disk
mass, though they may have disk masses adequate for the formation of
terrestrial-like planets.Comment: 32 pages, including 6 Postscript figures (TeX, uses psfig.sty); to
appear in "Protostars & Planets IV". Gif figures with captions and high-res
Postscript color figure available at
http://hven.swarthmore.edu/~jensen/preprints/ppiv.htm
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
Resolved Young Binary Systems And Their Disks
We have conducted a survey of young single and multiple systems in the Taurus–Auriga star-forming region with the Atacama Large Millimeter Array (ALMA), substantially improving both the spatial resolution and sensitivity with which individual protoplanetary disks in these systems have been observed. These ALMA observations can resolve binary separations as small as 25–30 au and have an average 3σ detection level of 0.35 mJy, equivalent to a disk mass of 4 × 10−5 M ⊙ for an M3 star. Our sample was constructed from stars that have an infrared excess and/or signs of accretion and have been classified as Class II. For the binary and higher-order multiple systems observed, we detect λ = 1.3 mm continuum emission from one or more stars in all of our target systems. Combined with previous surveys of Taurus, our 21 new detections increase the fraction of millimeter-detected disks to over 75% in all categories of stars (singles, primaries, and companions) earlier than spectral type M6 in the Class II sample. Given the wealth of other information available for these stars, this has allowed us to study the impact of multiplicity with a much larger sample. While millimeter flux and disk mass are related to stellar mass as seen in previous studies, we find that both primary and secondary stars in binary systems with separations of 30–4200 au have lower values of millimeter flux as a function of stellar mass than single stars. We also find that for these systems, the circumstellar disk around the primary star does not dominate the total disk mass in the system and contains on average 62% of the total mass
Resolved Young Binary Systems And Their Disks
We have conducted a survey of young single and multiple systems in the Taurus–Auriga star-forming region with the Atacama Large Millimeter Array (ALMA), substantially improving both the spatial resolution and sensitivity with which individual protoplanetary disks in these systems have been observed. These ALMA observations can resolve binary separations as small as 25–30 au and have an average 3σ detection level of 0.35 mJy, equivalent to a disk mass of 4 × 10−5 M ⊙ for an M3 star. Our sample was constructed from stars that have an infrared excess and/or signs of accretion and have been classified as Class II. For the binary and higher-order multiple systems observed, we detect λ = 1.3 mm continuum emission from one or more stars in all of our target systems. Combined with previous surveys of Taurus, our 21 new detections increase the fraction of millimeter-detected disks to over 75% in all categories of stars (singles, primaries, and companions) earlier than spectral type M6 in the Class II sample. Given the wealth of other information available for these stars, this has allowed us to study the impact of multiplicity with a much larger sample. While millimeter flux and disk mass are related to stellar mass as seen in previous studies, we find that both primary and secondary stars in binary systems with separations of 30–4200 au have lower values of millimeter flux as a function of stellar mass than single stars. We also find that for these systems, the circumstellar disk around the primary star does not dominate the total disk mass in the system and contains on average 62% of the total mass
The Connection between Submillimeter Continuum Flux and Binary Separation in Young Binaries: Evidence of Interaction between Stars and Disks
We present 800 micron continuum photometry of pre-main-sequence binary stars
with projected separations a_p < 150 AU in the Sco-Oph star-forming region.
Combining our observations with published 1300 micron photometry, we find that
binaries in Sco-Oph with 1 < a_p < 50--100 AU have lower submillimeter fluxes
than wider binaries or single stars, as previously found for Taurus- Auriga
binaries. The wide binaries and single stars have indistinguishable
submillimeter flux distributions. Thus, binary companions with separations less
than 50--100 AU significantly influence the nature of associated disks.
We have explored the hypothesis that the reduction in submillimeter flux is
the result of gaps cleared in disks by companions. Gap clearing produces the
qualitative dependence of submillimeter flux on binary separation, and a simple
model suggests that large gaps in disks with surface densities typical of
wide-binary or single-star disks can reduce submillimeter fluxes to levels
consistent with the observed limits. This model shows that the present
submillimeter flux upper limits do not necessarily imply a large reduction in
disk surface densities.
Two-thirds of the young binaries were detected by IRAS, showing that most
binaries have circumstellar disks. These fluxes place lower limits of 10^{-5}
M_sun on circumstellar disk masses. The submillimeter fluxes place upper limits
of 0.005 M_sun on circumbinary disk masses. Thus massive circumbinary disks are
rare among binaries with separations between a few AU and 100 AU. Circumbinary
disks are found around some close binaries.Comment: ApJ in press (Feb. 10, 1996). LaTeX, 35 pages, uses AASTeX macros.
Complete PostScript version with figures available from
http://www.astro.wisc.edu/prints/prints.html or by e-mail request to
[email protected]
Misaligned protoplanetary disks in a young binary star system
Many extrasolar planets follow orbits that differ from the nearly coplanar and circular orbits found in our Solar System; their orbits may be eccentric or inclined with respect to the host star’s equator, and the population of giant planets orbiting close to their host stars suggests appreciable orbital migration. There is at present no consensus on what produces such orbits. Theoretical explanations often invoke interactions with a binary companion star in an orbit that is inclined relative to the planet’s orbital plane. Such mechanisms require significant mutual inclinations between the planetary and binary star orbital planes. The protoplanetary disks in a few young binaries are misaligned, but often the measurements of these misalignments are sensitive only to a small portion of the inner disk, and the three-dimensional misalignment of the bulk of the planet-forming disk mass has hitherto not been determined. Here we report that the protoplanetary disks in the young binary system HK Tauri are misaligned by 60 to 68 degrees, such that one or both of the disks are significantly inclined to the binary orbital plane. Our results demonstrate that the necessary conditions exist for misalignment-driven mechanisms to modify planetary orbits, and that these conditions are present at the time of planet formation, apparently because of the binary formation process
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