46 research outputs found
A 4 Gyr M-dwarf Gyrochrone from CFHT/MegaPrime Monitoring of the Open Cluster M67
We present stellar rotation periods for late K- and early M-dwarf members of
the 4 Gyr old open cluster M67 as calibrators for gyrochronology and tests of
stellar spin-down models. Using Gaia EDR3 astrometry for cluster membership and
Pan-STARRS (PS1) photometry for binary identification, we build this set of
rotation periods from a campaign of monitoring M67 with the
Canada-France-Hawaii Telescope's MegaPrime wide field imager. We identify 1807
members of M67, of which 294 are candidate single members with significant
rotation period detections. Moreover, we fit a polynomial to the period versus
color-derived effective temperature sequence observed in our data. We find that
the rotation of very cool dwarfs can be explained by a simple solid-body
spin-down between 2.7 and 4 Gyr. We compare this rotational sequence to the
predictions of gyrochronological models and find that the best match is
Skumanich-like spin-down, P_rot \propto t^0.62, applied to the sequence of
Ruprecht 147. This suggests that, for spectral types K7-M0 with near-solar
metallicity, once a star resumes spinning down, a simple Skumanich-like is
sufficient to describe their rotation evolution, at least through the age of
M67. Additionally, for stars in the range M1-M3, our data show that spin-down
must have resumed prior to the age of M67, in conflict with predictions of the
latest spin-down models.Comment: 21 pages, 16 figures, Accepted for publication by Ap
The splitting of double-component active asteroid P/2016 J1 (PANSTARRS)
We present deep imaging observations, orbital dynamics, and dust tail model
analyses of the double-component asteroid P/2016 J1 (J1-A and J1-B). The
observations were acquired at the Gran Telescopio Canarias (GTC) and the
Canada-France-Hawaii Telescope (CFHT) from mid March to late July, 2016. A
statistical analysis of backward-in-time integrations of the orbits of a large
sample of clone objects of P/2016 J1-A and J1-B shows that the minimum
separation between them occurred most likely 2300 days prior to the
current perihelion passage, i.e., during the previous orbit near perihelion.
This closest approach was probably linked to a fragmentation event of their
parent body. Monte Carlo dust tail models show that those two components became
active simultaneously 250 days before the current perihelion, with
comparable maximum loss rates of 0.7 kg s and 0.5 kg
s, and total ejected masses of 810 kg and
610 kg for fragments J1-A and J1-B, respectively. In consequence,
the fragmentation event and the present dust activity are unrelated. The
simultaneous activation times of the two components and the fact that the
activity lasted 6 to 9 months or longer, strongly indicate ice sublimation as
the most likely mechanism involved in the dust emission process.Comment: Accepted by ApJ Letters, Feb. 17, 201
Core repulsion effects in alkali trimers
The present paper is related to a talk presented during the Symposium on
Coherent Control and Ultracold Chemistry held during the Sixth Congress of the
International Society for Theoretical Chemical Physics (ISTCP-VI, July 2008).
The talk was entitled "Electronic structure properties of alkali dimers and
trimers. Prospects for alignment of ultracold molecules". Here we report on the
electrostatic repulsion forces of the ionic cores at short separation, involved
when the potential energy surfaces of alkali trimers are calculated with a
quantum chemistry approach based on effective large-core potentials for ionic
core description. We demonstrate that such forces in the triatomic molecule can
be obtained as the sum of three pairwise terms. We illustrate our results on
the lowest electronic states of Cs, which are computed for the first time
within a full configuration interaction based on a large Gaussian basis set. As
a preliminary section, we also propose a brief introduction about the
importance of alkali trimer systems in the context of cold and ultracold
molecules
The Robo-AO-2 facility for rapid visible/near-infrared AO imaging and the demonstration of hybrid techniques
We are building a next-generation laser adaptive optics system, Robo-AO-2,
for the UH 2.2-m telescope that will deliver robotic, diffraction-limited
observations at visible and near-infrared wavelengths in unprecedented numbers.
The superior Maunakea observing site, expanded spectral range and rapid
response to high-priority events represent a significant advance over the
prototype. Robo-AO-2 will include a new reconfigurable natural guide star
sensor for exquisite wavefront correction on bright targets and the
demonstration of potentially transformative hybrid AO techniques that promise
to extend the faintness limit on current and future exoplanet adaptive optics
systems.Comment: 15 page
Analysis of Neptune's 2017 Bright Equatorial Storm
We report the discovery of a large (8500 km diameter) infrared-bright
storm at Neptune's equator in June 2017. We tracked the storm over a period of
7 months with high-cadence infrared snapshot imaging, carried out on 14 nights
at the 10 meter Keck II telescope and 17 nights at the Shane 120 inch reflector
at Lick Observatory. The cloud feature was larger and more persistent than any
equatorial clouds seen before on Neptune, remaining intermittently active from
at least 10 June to 31 December 2017. Our Keck and Lick observations were
augmented by very high-cadence images from the amateur community, which
permitted the determination of accurate drift rates for the cloud feature. Its
zonal drift speed was variable from 10 June to at least 25 July, but remained a
constant m s from 30 September until at least 15
November. The pressure of the cloud top was determined from radiative transfer
calculations to be 0.3-0.6 bar; this value remained constant over the course of
the observations. Multiple cloud break-up events, in which a bright cloud band
wrapped around Neptune's equator, were observed over the course of our
observations. No "dark spot" vortices were seen near the equator in HST imaging
on 6 and 7 October. The size and pressure of the storm are consistent with
moist convection or a planetary-scale wave as the energy source of convective
upwelling, but more modeling is required to determine the driver of this
equatorial disturbance as well as the triggers for and dynamics of the observed
cloud break-up events.Comment: 42 pages, 14 figures, 6 tables; Accepted to Icaru