40 research outputs found
Accreting Protoplanets in the LkCa 15 Transition Disk
Exoplanet detections have revolutionized astronomy, offering new insights
into solar system architecture and planet demographics. While nearly 1900
exoplanets have now been discovered and confirmed, none are still in the
process of formation. Transition discs, protoplanetary disks with inner
clearings best explained by the influence of accreting planets, are natural
laboratories for the study of planet formation. Some transition discs show
evidence for the presence of young planets in the form of disc asymmetries or
infrared sources detected within their clearings, as in the case of LkCa 15.
Attempts to observe directly signatures of accretion onto protoplanets have
hitherto proven unsuccessful. Here we report adaptive optics observations of
LkCa 15 that probe within the disc clearing. With accurate source positions
over multiple epochs spanning 2009 - 2015, we infer the presence of multiple
companions on Keplerian orbits. We directly detect H{\alpha} emission from the
innermost companion, LkCa 15 b, evincing hot (~10,000 K) gas falling deep into
the potential well of an accreting protoplanet.Comment: 35 pages, 3 figures, 1 table, 9 extended data item
Betelgeuse scope: Single-mode-fibers-assisted optical interferometer design for dedicated stellar activity monitoring
This is the final version. Available from SPIE via the DOI in this recordBetelgeuse has experienced a sudden shift in its brightness and dimmed mysteriously. This is likely caused by a hot blob of plasma ejected from Betelgeuse and then cooled to obscuring dust. If true, it is a remarkable opportunity to directly witness the formation of dust around a red supergiant star. Today's optical telescope facilities are not optimized for monitoring the Betelgeuse surface, so in this work, we propose a low-cost optical interferometer. The facility will consist of 12 x 4 inch optical telescopes mounted to the surface of a large radio dish for model-independent aperture synthesis imaging; polarization-maintaining single-mode fibers will carry the coherent beams from the individual optical telescopes to an all-in-one beam combiner. A fast steering mirror assisted fiber injection system guides the flux into fibers. A metrology system senses vibration-induced piston errors in optical fibers, and these errors are corrected using fast-steering delay lines. We will present the design.Steward Observatory Fellowship in Instrumentation and Technology Development
Stellar Multiplicity
Stellar multiplicity is an ubiquitous outcome of the star formation process.
Characterizing the frequency and main characteristics of multiple systems and
their dependencies on primary mass and environment is therefore a powerful tool
to probe this process. While early attempts were fraught with selection biases
and limited completeness, instrumentation breakthroughs in the last two decades
now enable robust analyses. In this review, we summarize our current empirical
knowledge of stellar multiplicity for Main Sequence stars and brown dwarfs, as
well as among populations of Pre-Main Sequence stars and embedded protostars.
Clear trends as a function of both primary mass and stellar evolutionary stage
are identified that will serve as a comparison basis for numerical and
analytical models of star formation.Comment: original version submitted to ARA&A, final version to appear in vol.
51, comments welcome, 38 pages, 5 figure
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The HOSTS Survey for Exozodiacal Dust: Preliminary results and future prospects
[abridged] The presence of large amounts of dust in the habitable zones of
nearby stars is a significant obstacle for future exo-Earth imaging missions.
We executed an N band nulling interferometric survey to determine the typical
amount of such exozodiacal dust around a sample of nearby main sequence stars.
The majority of our data have been analyzed and we present here an update of
our ongoing work. We find seven new N band excesses in addition to the high
confidence confirmation of three that were previously known. We find the first
detections around Sun-like stars and around stars without previously known
circumstellar dust. Our overall detection rate is 23%. The inferred occurrence
rate is comparable for early type and Sun-like stars, but decreases from 71%
[+11%/-20%] for stars with previously detected mid- to far-infrared excess to
11% [+9%/-4%] for stars without such excess, confirming earlier results at high
confidence. For completed observations on individual stars, our sensitivity is
five to ten times better than previous results. Assuming a lognormal luminosity
function of the dust, we find upper limits on the median dust level around all
stars without previously known mid to far infrared excess of 11.5 zodis at 95%
confidence level. The corresponding upper limit for Sun-like stars is 16 zodis.
An LBTI vetted target list of Sun-like stars for exo-Earth imaging would have a
corresponding limit of 7.5 zodis. We provide important new insights into the
occurrence rate and typical levels of habitable zone dust around main sequence
stars. Exploiting the full range of capabilities of the LBTI provides a
critical opportunity for the detailed characterization of a sample of
exozodiacal dust disks to understand the origin, distribution, and properties
of the dust.GMK is supported by the Royal Society as a Royal Society University Research Fellow. AS is partially supported by funding from the Center for Exoplanets and Habitable Worlds. The Center for Exoplanets and
Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium. JMS is supported by NASA through Hubble Fellowship grant HSTHF2-51398.001-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
The HOSTS Survey for Exozodiacal Dust: Observational Results from the Complete Survey
The Large Binocular Telescope Interferometer (LBTI) enables nulling
interferometric observations across the N band (8 to 13 um) to suppress a
star's bright light and probe for faint circumstellar emission. We present and
statistically analyze the results from the LBTI/HOSTS (Hunt for Observable
Signatures of Terrestrial Systems) survey for exozodiacal dust. By comparing
our measurements to model predictions based on the Solar zodiacal dust in the N
band, we estimate a 1 sigma median sensitivity of 23 zodis for early type stars
and 48 zodis for Sun-like stars, where 1 zodi is the surface density of
habitable zone (HZ) dust in the Solar system. Of the 38 stars observed, 10 show
significant excess. A clear correlation of our detections with the presence of
cold dust in the systems was found, but none with the stellar spectral type or
age. The majority of Sun-like stars have relatively low HZ dust levels
(best-fit median: 3 zodis, 1 sigma upper limit: 9 zodis, 95% confidence: 27
zodis based on our N band measurements), while ~20% are significantly more
dusty. The Solar system's HZ dust content is consistent with being typical. Our
median HZ dust level would not be a major limitation to the direct imaging
search for Earth-like exoplanets, but more precise constraints are still
required, in particular to evaluate the impact of exozodiacal dust for the
spectroscopic characterization of imaged exo-Earth candidates
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The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10 to 100 au
We present a statistical analysis of the first 300 stars observed by the
Gemini Planet Imager Exoplanet Survey (GPIES). This subsample includes six
detected planets and three brown dwarfs; from these detections and our contrast
curves we infer the underlying distributions of substellar companions with
respect to their mass, semi-major axis, and host stellar mass. We uncover a
strong correlation between planet occurrence rate and host star mass, with
stars M 1.5 more likely to host planets with masses between 2-13
M and semi-major axes of 3-100 au at 99.92% confidence. We fit a
double power-law model in planet mass (m) and semi-major axis (a) for planet
populations around high-mass stars (M 1.5M) of the form , finding = -2.4 0.8 and
= -2.0 0.5, and an integrated occurrence rate of %
between 5-13 M and 10-100 au. A significantly lower occurrence rate
is obtained for brown dwarfs around all stars, with 0.8% of
stars hosting a brown dwarf companion between 13-80 M and 10-100
au. Brown dwarfs also appear to be distributed differently in mass and
semi-major axis compared to giant planets; whereas giant planets follow a
bottom-heavy mass distribution and favor smaller semi-major axes, brown dwarfs
exhibit just the opposite behaviors. Comparing to studies of short-period giant
planets from the RV method, our results are consistent with a peak in
occurrence of giant planets between ~1-10 au. We discuss how these trends,
including the preference of giant planets for high-mass host stars, point to
formation of giant planets by core/pebble accretion, and formation of brown
dwarfs by gravitational instability
Recommended from our members
The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10 to 100 au
We present a statistical analysis of the first 300 stars observed by the
Gemini Planet Imager Exoplanet Survey (GPIES). This subsample includes six
detected planets and three brown dwarfs; from these detections and our contrast
curves we infer the underlying distributions of substellar companions with
respect to their mass, semi-major axis, and host stellar mass. We uncover a
strong correlation between planet occurrence rate and host star mass, with
stars M 1.5 more likely to host planets with masses between 2-13
M and semi-major axes of 3-100 au at 99.92% confidence. We fit a
double power-law model in planet mass (m) and semi-major axis (a) for planet
populations around high-mass stars (M 1.5M) of the form , finding = -2.4 0.8 and
= -2.0 0.5, and an integrated occurrence rate of %
between 5-13 M and 10-100 au. A significantly lower occurrence rate
is obtained for brown dwarfs around all stars, with 0.8% of
stars hosting a brown dwarf companion between 13-80 M and 10-100
au. Brown dwarfs also appear to be distributed differently in mass and
semi-major axis compared to giant planets; whereas giant planets follow a
bottom-heavy mass distribution and favor smaller semi-major axes, brown dwarfs
exhibit just the opposite behaviors. Comparing to studies of short-period giant
planets from the RV method, our results are consistent with a peak in
occurrence of giant planets between ~1-10 au. We discuss how these trends,
including the preference of giant planets for high-mass host stars, point to
formation of giant planets by core/pebble accretion, and formation of brown
dwarfs by gravitational instability
Qualitative assessment of the long-term impact of a faculty development programme in teaching skills
Faculty Development in Veterinary Education: Are We Doing Enough (or Publishing Enough About It), and Do We Value It?
Catriona Bell – ORCID: 0000-0001-8501-1697
https://orcid.org/0000-0001-8501-1697Item not available in this repository.In this discussion article, I aim to promote international discourse about faculty development in veterinary education, to highlight both the paucity of literature available in this field and the variation in terminology used in publications, to draw from existing evidence in medical education literature, and to identify what we know already and where we are now and where we should be in the next 10 years.https://doi.org/10.3138/jvme.0113-022R40pubpub