1,080 research outputs found
The Periodic Spectroscopic Variability of FU Orionis
FU Orionis systems are young stars undergoing outbursts of disc accretion and
where the optical spectrum contains lines associated with both the disc
photosphere and a wind component. Previous observations of the prototype FU
Orionis have suggested that the wind lines and the photospheric lines are
modulated with periods of 14.54 and 3.54 days respectively (Herbig et al.
2003). We have re-observed the system at higher spectral resolution, by
monitoring variations of optical line profiles over 21 nights in 2007 and have
found periods of 13.48 and 3.6 days in the wind and disc components consistent
with the above: this implies variability mechanisms that are stable over at
least a decade. In addition we have found: i) that the variations in the
photospheric absorption lines are confined to the blue wing of the line (around
-9km/s): we tentatively ascribe this to an orbiting hotspot in the disc which
is obscured by a disc warp during its receding phase. ii) The wind period is
manifested not only in blue-shifted Halpha absorption, but also in red-shifted
emission of Halpha and Hbeta, as well as in blue-shifted absorption of Na I D,
Li I and Fe II. iii) We find that the periodic modulation of blue-shifted
Halpha absorption at around -100km/s, is phase lagged with respect to
variations in the other lines by ~1.8days. This is consistent with a picture in
which variations at the wind base first affect chromospheric emission and then
low velocity blue-shifted absorption, followed - after a lag equal to the
propagation time of disturbances across the wind's acceleration region - by a
response in high velocity blue-shifted absorption. Such arguments constrain the
size of the acceleration region to ~10^12cm. We discuss possible mechanisms for
periodic variations within the innermost 0.1AU of the disc, including the
possibility that these variations indicate the presence of an embedded hot
Jupiter.Comment: 20 pages, 23 figures. Accepted for publication in MNRAS. See
http://www.ast.cam.ac.uk/~slp65/FUOripaperHRes.pdf for a pdf version of the
paper with high-resolution images; footnote added to the titl
High-resolution spectroscopy of QY Sge -- An obscured RV Tauri variable?
The first high-resolution optical spectra of QY Sge are presented and
discussed. Menzies & Whitelock (1988) on the basis of photometry and
low-resolution spectra suggested that this G0I supergiant was obscured by dust
and seen only by scattered light from a circumstellar reflection nebula. The
new spectra confirm and extend this picture. Photospheric lines are unusually
broad indicating scattering of photons from dust in the stellar wind. Presence
of very broad Na D emission lines is confirmed. Sharp emission lines from low
levels of abundant neutral metal atoms are reported for the first time. An
abundance analysis of photospheric lines shows that the stellar atmosphere is
of approximately solar composition but with highly condensible (e.g., Sc and
Ti) elements depleted by factors of 5 to 10.Comment: 8 pages, 9 figures, accepted for publication in MNRA
X-ray Emission from the FU Orionis Star V1735 Cygni
The variable star V1735 Cyg (= Elias 1-12) lies in the IC 5146 dark cloud and
is a member of the class of FU Orionis objects whose dramatic optical
brightenings are thought to be linked to episodic accretion. We report the
first X-ray detections of V1735 Cyg and a deeply-embedded class I protostar
lying 24 arcsecs to its northeast. X-ray spectra obtained with EPIC on
XMM-Newton reveal very high-temperature plasma (kT > 5 keV) in both objects,
but no large flares. Such hard X-ray emission is not anticipated from accretion
shocks and is a signature of magnetic processes. We place these new results
into the context of what is presently known about the X-ray properties of FU
Orionis stars and other accreting young stellar objects.Comment: 25 pages, 6 figure
Fundamental Vibrational Transition of CO During the Outburst of EX Lupi in 2008
We report monitoring observations of the T Tauri star EX Lupi during its outburst in 2008 in the CO fundamental
band at 4.6–5.0 μm. The observations were carried out at the Very Large Telescope and the Subaru Telescope at six
epochs from 2008 April to August, covering the plateau of the outburst and the fading phase to a quiescent state.
The line flux of CO emission declines with the visual brightness of the star and the continuum flux at 5 μm, but
composed of two subcomponents that decay with different rates. The narrow-line emission (50 kms^(−1) in FWHM) is
near the systemic velocity of EX Lupi. These emission lines appear exclusively in v =1–0. The line widths translate
to a characteristic orbiting radius of 0.4 AU. The broad-line component (FWZI ~ 150 km s^(−1)) is highly excited up
to v ≤ 6. The line flux of the component decreases faster than the narrow-line emission. Simple modeling of the
line profiles implies that the broad-line emitting gas is orbiting around the star at 0.04–0.4 AU. The excitation state, the decay speed of the line flux, and the line profile indicate that the broad-line emission component is physically distinct from the narrow-line emission component, and more tightly related to the outburst event
Trajectories of Experience Through the Pandemic: A Qualitative Longitudinal Dataset
Here, we present a dataset collected within a longitudinal interview study that has been conducted as part of a larger project (i.e., Viral Communication), exploring (changing) public attitudes and behaviours through the course of the pandemic in Germany. From a nationally representative survey, forty participants were purposively sampled on the basis of gender, age and socioeconomic status for the interviews. Each participant was interviewed three times within a 10 month time frame (between December 2020 and September 2021), with the exception of two dropouts from the study. The semi-structured interviews were developed to further elaborate on some of the responses in the survey instrument and to provide additional insights into topics and controversies surrounding the Covid-19 pandemic in Germany, such as information/misinformation, trust/distrust, compliance, vaccination, and conspiracy beliefs
Mapping the CMB I: the first flight of the QMAP experiment
We report on the first flight of the balloon-borne QMAP experiment. The
experiment is designed to make a map of the cosmic microwave background
anisotropy on angular scales from 0.7 to several degrees. Using the map we
determine the angular power spectrum of the anisotropy in multipole bands from
l~40 to l~140. The results are consistent with the Saskatoon (SK) measurements.
The frequency spectral index (measured at low l) is consistent with that of CMB
and inconsistent with either Galactic synchrotron or free-free emission. The
instrument, measurement, analysis of the angular power spectrum, and possible
systematic errors are discussed.Comment: 4 pages, with 5 figures included. Submitted to ApJL. Window functions
and color figures are available at
http://pupgg.princeton.edu/~cmb/welcome.htm
Gauge symmetry of linearised Nordström gravity and the dual spin two field theory
The field equations are proposed for the third rank tensor field with the hook Young diagram. The equations describe the irreducible spin two massless representation in any d ≥ 3. The starting point of the construction is the linearised system of Einstein equations which includes the Nordström equation. This equation, being considered irrespectively to the rest of the Einstein system, corresponds to the topological field theory. The general solution is a pure gauge, modulo topological modes which we neglect in this article. We find the sequence of the reducible gauge transformations for the linearised Nordström equation, with the hook tensor being the initial gauge symmetry parameter. By substituting the general solution of the Nordström equation into the rest of the Einstein’s system, we arrive at the field equations for the hook tensor. The degree of freedom number count confirms, it is the spin two theory
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