57 research outputs found
Bipolar jets produced by a spectroscopic binary
We present evidence that the spectroscopically identified bipolar jets of the
pre-main sequence binary KH 15D are a common product of the whole binary
system, rather than being launched from either star individually. They may be
launched from the innermost part of the circumbinary disk (CBD) or may result
from the merging of two outflows driven by the individual stars. This evidence
is based on high-resolution H-alpha and [OI] 6300A line profiles obtained
during eclipse phases of this nearly edge-on system. The occultation of star A
(the only currently visible star) by the disk strongly suppresses the stellar
H-alpha and continuum emission and allows one to study the faint redshifted and
blueshifted emission components of the bipolar jets. The strongest evidence for
jet production by the whole binary system comes from the observed radial
velocity symmetry of the two jet components relative to the systemic velocity
of the binary, in combination with current accretion models from the CBD onto a
binary system.Comment: ApJ Letters, in press [6 pages
Natural Coronagraphic Observations of the Eclipsing T Tauri System KH 15D: Evidence for Accretion and Bipolar Outflow in a WTTS
We present high resolution (R 44,000) UVES spectra of the eclipsing
pre-main sequence star KH 15D covering the wavelength range 4780 to 6810 {\AA}
obtained at three phases: out of eclipse, near minimum light and during egress.
The system evidently acts like a natural coronagraph, enhancing the contrast
relative to the continuum of hydrogen and forbidden emission lines during
eclipse. At maximum light the H equivalent width was 2 {\AA} and
the profile showed broad wings and a deep central absorption. During egress the
equivalent width was much higher (70 {\AA}) and the broad wings, which
extend to 300 km/s, were prominent. During eclipse totality the
equivalent width was less than during egress (40 {\AA}) and the high
velocity wings were much weaker. H showed a somewhat different behavior,
revealing only the blue-shifted portion of the high velocity component during
eclipse and egress. [OI] 6300, 6363 lines are easily seen both
out of eclipse and when the photosphere is obscured and exhibit little or no
flux variation with eclipse phase. Our interpretation is that KH 15D, although
clearly a weak-line T Tauri star by the usual criteria, is still accreting
matter from a circumstellar disk, and has a well-collimated bipolar jet. As the
knife-edge of the occulting matter passes across the close stellar environment
it is evidently revealing structure in the magnetosphere of this pre-main
sequence star with unprecedented spatial resolution. We also show that there is
only a small, perhaps marginally significant, change in the velocity of the K7
star between the maximum light and egress phases probed here
The Light Curve of the Weakly-Accreting T Tauri Binary KH 15D from 2005-10: Insights into the Nature of its Protoplanetary Disk
Photometry of the unique pre-main sequence binary system KH 15D is presented,
spanning the years 2005-2010. This system has exhibited photometric variations
and eclipses over the last 50 years caused by a precessing circumbinary disk.
Advancement of the occulting edge across the binary orbit has continued and the
photospheres of both stars are now completely obscured at all times. The system
is now visible only by scattered light, and yet it continues to show a periodic
variation on the orbital cycle with an amplitude exceeding two magnitudes. This
variation, which depends only on the binary phase, has likely been present in
the data since at least 1995. It can, by itself, account for shoulders on the
light curve prior to ingress and following egress, obviating the need for
components of extant models such as a scattering halo around star A or forward
scattering from a fuzzy disk edge. A plausible source for the variable
scattering component is reflected light from the far side of a warped occulting
disk. We have detected color changes in V-I of several tenths of a magnitude to
both the blue and red that occur during times of minima. These may indicate the
presence of a third source of light (faint star) within the system, or a change
in the reflectance properties of the disk as the portion being illuminated
varies with the orbital motion of the stars. The data support a picture of the
circumbinary disk as a geometrically thin, optically thick layer of perhaps mm
or cm-sized particles that has been sculpted by the binary stars and possibly
other components into a decidedly nonplanar configuration. A simple (infinitely
sharp) knife-edge model does a good job of accounting for all of the recent
(2005-2010) occultation data.Comment: To appear in The Astronomical Journa
Multi-wavelength observations of the peculiar red giant HR 3126
Ultraviolet observations of the red giant HR 3126 are combined with multi-wavelength data in order to provide a firmer basis for explaining the arc-minute sized nebula surrounding the object. Possibilities as to the location of HR 3126 on the Hertzsprung-Russel diagram, and to the formation mechanisms of the reflection nebula IC 2220 associated with it, are summarized
Violation of the `Zero-Force Theorem' in the time-dependent Krieger-Li-Iafrate approximation
We demonstrate that the time-dependent Krieger-Li-Iafrate approximation in
combination with the exchange-only functional violates the `Zero-Force
Theorem'. By analyzing the time-dependent dipole moment of Na5 and Na9+, we
furthermore show that this can lead to an unphysical self-excitation of the
system depending on the system properties and the excitation strength.
Analytical aspects, especially the connection between the `Zero-Force Theorem'
and the `Generalized-Translation Invariance' of the potential, are discussed.Comment: 5 pages, 4 figure
Multiband photometric detection of a huge flare on the M9 dwarf 2MASSW J1707183+643933
We present simultaneous UV-G-R-I monitoring of 19 M dwarfs that revealed a
huge flare on the M9 dwarf 2MASSW J1707183+643933 with an amplitude in the UV
of at least 6 magnitudes. This is one of the strongest detections ever of an
optical flare on an M star and one of the first in an ultracool dwarf (UCD,
spectral types later than about M7). Four intermediate strength flares (Delta
m_UV < 4 mag) were found in this and three other targets. For the whole sample
we deduce a flare probability of 0.013 (rate of 0.018/hr), and 0.049 (0.090/hr)
for 2M1707+64 alone. Deviations of the flare emission from a blackbody is
consistent with strong Halpha line emission. We also confirm the previously
found rotation period for 2M1707+64 (Rockenfeller, Bailer-Jones & Mundt (2006),
http://arxiv.org/abs/astro-ph/0511614/) and determine it more precisely to be
3.619 +/- 0.015 hr.Comment: Accepted to MNRAS. Five page
Complex Variability of the H Emission Line Profile of the T Tauri Binary System KH 15D: The Influence of Orbital Phase, Occultation by the Circumbinary Disk, and Accretion Phenomenae
We have obtained 48 high resolution echelle spectra of the pre-main sequence
eclipsing binary system KH~15D (V582 Mon, P = 48.37 d, 0.6, M
= 0.6 M, M = 0.7 M). The eclipses are caused by a
circumbinary disk seen nearly edge on, which at the epoch of these observations
completely obscured the orbit of star B and a large portion of the orbit of
star A. The spectra were obtained over five contiguous observing seasons from
2001/2002 to 2005/2006 while star A was fully visible, fully occulted, and
during several ingress and egress events. The H line profile shows
dramatic changes in these time series data over timescales ranging from days to
years. A fraction of the variations are due to "edge effects" and depend only
on the height of star A above or below the razor sharp edge of the occulting
disk. Other observed variations depend on the orbital phase: the H
emission line profile changes from an inverse P Cygni type profile during
ingress to an enhanced double-peaked profile, with both a blue and red emission
component, during egress. Each of these interpreted variations are complicated
by the fact that there is also a chaotic, irregular component present in these
profiles. We find that the complex data set can be largely understood in the
context of accretion onto the stars from a circumbinary disk with gas flows as
predicted by the models of eccentric T Tauri binaries put forward by Artymowicz
& Lubow, G\"{u}nther & Kley, and de Val-Borro et al. In particular, our data
provide strong support for the pulsed accretion phenomenon, in which enhanced
accretion occurs during and after perihelion passage.Comment: accepted to Ap
HST/STIS Spectroscopy of the Optical Outflow from DG Tau: Indications for Rotation in the Initial Jet Channel
We have carried out a kinematical, high angular resolution (~ 0".1) study of
the jet from DG Tau within 0."5 from the source (or 110 AU along this flow). We
analysed line profiles extracted from a set of seven spectra taken with STIS on
board the Hubble Space Telescope, with the slits parallel to the jet axis but
displaced transversely every 0".07. For the flow of moderate velocity (-70
km/s), we have found systematic differences in the radial velocities of lines
emitted on alternate sides of the jet axis. The results are corrected for the
effects due to uneven illumination of the slit. The relative Doppler shifts
range from 5 to 20 km/s. If this is interpreted as rotation, the flow is then
rotating clockwise looking from the jet towards the source and the derived
toroidal velocities are in the range 6 - 15 km/s. Using recent estimates of the
mass loss rate, one obtains for the considered velocity regime, an angular
momentum flux of ~ 3.8x10E-5 M_sun/yr AU km/s. Our findings may constitute the
first detection of rotation in the initial channel of a jet flow. The derived
values appear to be consistent with the predictions of popular
magneto-centrifugal jet-launching models, although we cannot exclude transverse
outflow asymmetries other than rotation.Comment: aastex, 23 pages, 5 b/w figures, 3 color figures, ApJ in pres
Fine Structure in the Circumstellar Environment of a Young, Solar-like Star: the Unique Eclipses of KH 15D
Results of an international campaign to photometrically monitor the unique
pre-main sequence eclipsing object KH 15D are reported. An updated ephemeris
for the eclipse is derived that incorporates a slightly revised period of 48.36
d. There is some evidence that the orbital period is actually twice that value,
with two eclipses occurring per cycle. The extraordinary depth (~3.5 mag) and
duration (~18 days) of the eclipse indicate that it is caused by circumstellar
matter, presumably the inner portion of a disk. The eclipse has continued to
lengthen with time and the central brightness reversals are not as extreme as
they once were. V-R and V-I colors indicate that the system is slightly bluer
near minimum light. Ingress and egress are remarkably well modeled by the
passage of a knife-edge across a limb-darkened star. Possible models for the
system are briefly discussed.Comment: 19 pages, 5 figure
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