813 research outputs found
Profiles of Strong Permitted Lines in Classical T Tauri Stars
We present a spectral analysis of 30 T Tauri stars observed with the Hamilton
echelle spectrograph over more than a decade. One goal is to test
magnetospheric accretion model predictions. Observational evidence previously
published supporting the model, such as emission line asymmetry and a high
frequency of redshifted absorption components, are considered. We also discuss
the relation between different line forming regions and search for good
accretion rate indicators.
In this work we confirm several important points of the models, such as the
correlation between accretion and outflow, broad emission components that are
mostly central or slightly blueshifted and only the occasional presence of
redshifted absorption. We also show, however, that the broad emission
components supposedly formed in the magnetospheric accretion flow only
partially support the models. Unlike the predictions, they are sometimes
redshifted, and are mostly found to be symmetric. The published theoretical
profiles do not have a strong resemblance to our observed ones. We emphasize
the need for accretion models to include a strong turbulent component before
their profiles will match the observations. The effects of rotation, and the
outflow components, will also be needed to complete the picture.Comment: 25 pages including 9 figures, 3 tables, accepted for publication in
the Astronomical Journa
When does the zero fiber of the moment map have rational singularities?
Let be a complex reductive group and a -module. There is a natural
moment mapping and we denote
(the shell) by . We use invariant theory and results of
Musta\c{t}\u{a} [Mus01] to find criteria for to have rational
singularities and for the categorical quotient to have
symplectic singularities, the latter results improving upon [HSS20]. It turns
out that for ``most'' -modules , the shell has rational
singularities. For the case of direct sums of classical representations of the
classical groups, has rational singularities and has
symplectic singularities if is a reduced and irreducible complete
intersection. Another important special case is (the direct
sum of copies of the Lie algebra of ) where . We show that
has rational singularities and that has symplectic
singularities, improving upon results of [Bud19], [AA16], [Kap19] and [GH20].
Let where is a closed Riemann surface of genus
. Let be semisimple and let and
be the corresponding representation variety and character
variety. We show that is a complete intersection
with rational singularities and that has symplectic
singularities. If or contains no simple factor of rank , then the
singularities of and are in
codimension at least four and is locally factorial.
If, in addition, is simply connected, then is locally
factorial.Comment: 21 pages. v2: 22 pages, clarified and improved arguments in Section
3, improved exposition and minor corrections. v3: 30 pages, reformatted,
minor correction
V1647 Ori (IRAS 05436-0007) in Outburst: the First Three Months
We report on photometric (BVRIJHK) and low dispersion spectroscopic
observations of V1647 Ori, the star that drives McNeil's Nebula, between 10
February and 7 May 2004. The star is photometrically variable atop a general
decline in brightness of about 0.3-0.4 magnitudes during these 87 days. The
spectra are featureless, aside from H-alpha and the Ca II infrared triplet in
emission, and a Na I D absorption feature. The Ca II triplet line ratios are
typical of young stellar objects. The H-alpha equivalent width may be modulated
on a period of about 60 days. The post-outburst extinction appears to be less
than 7 mag. The data are suggestive of an FU Orionis-like event, but further
monitoring will be needed to definitively characterize the outburst.Comment: Accepted for publication in the Astronomical Journa
Mapping the CMB II: the second flight of the QMAP experiment
We report the results from the second flight of QMAP, an experiment to map
the cosmic microwave background near the North Celestial Pole. We present maps
of the sky at 31 and 42 GHz as well as a measurement of the angular power
spectrum covering the l-range 40-200. Anisotropy is detected at about 20 sigma
and is in agreement with previous results at these angular scales. We also
report details of the data reduction and analysis techniques which were used
for both flights of QMAP.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
Critical Rhetoric and Collaboration: Missing Principle #9 and ProfsDoPop.com
As part of this Special Section on critical rhetoric, this article examines the role of collaboration in the future of critical rhetoric. Building on McKerrow’s original eight principles of praxis, the authors advocate for a missing ninth principle that reflects the need for critical rhetoric to be a shared venture across both individual projects and larger discourses. As an example of this type of work, they provide ProfsDoPop.com, an academic, online blog designed to bring academic sensibilities and concepts to popular audiences through the critique of popular culture
A Measurement of the Angular Power Spectrum of the CMB from l = 100 to 400
We report on a measurement of the angular spectrum of the CMB between
and made at 144 GHz from Cerro Toco in the
Chilean altiplano. When the new data are combined with previous data at 30 and
40 GHz, taken with the same instrument observing the same section of sky, we
find: 1) a rise in the angular spectrum to a maximum with K at and a fall at , thereby localizing the peak
near ; and 2) that the anisotropy at has the
spectrum of the CMB.Comment: 4 pages, 2 figures. Revised version; includes Ned Wright's postscript
fix. Accepted by ApJL. Website at http://physics.princeton.edu/~cmb
Stellar contents and star formation in the young star cluster Be 59
We present CCD photometry of the young open cluster Be 59 with the
aim to study the star formation scenario in the cluster. The radial extent of
the cluster is found to be 10 arcmin (2.9 pc). The interstellar
extinction in the cluster region varies between 1.4 to 1.8 mag.
The ratio of total-to-selective extinction in the cluster region is estimated
as . The distance of the cluster is found to be kpc.
Using near-infrared colours and slitless spectroscopy, we have identified young
stellar objects (YSOs) in the open cluster Be 59 region. The ages of these YSOs
range between Myr to 2 Myr, whereas the mean age of the massive
stars in the cluster region is found to be 2 Myr. There is evidence for
second generation star formation outside the boundary of the cluster, which may
be triggered by massive stars in the cluster. The slope of the initial mass
function, , in the mass range is found to be
which is shallower than the Salpeter value (-1.35), whereas in
the mass range the slope is almost flat. The slope of
the K-band luminosity function is estimated as , which is smaller
than the average value (0.4) reported for young embedded clusters.
Approximately 32% of H emission stars of Be 59 exhibit NIR excess
indicating that inner disks of the T-Tauri star (TTS) population have not
dissipated. The MSX and IRAS-HIRES images around the cluster region are also
used to study the emission from unidentified infrared bands and to estimate the
spatial distribution of optical depth of warm and cold interstellar dust.Comment: Accepted for the publication in MNRAS, 39 pages, 26 Figures, 8 Table
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