21 research outputs found
The K2-ESPRINT Project III: A Close-in Super-Earth around a Metal-rich Mid-M Dwarf
We validate a planet on a close-in orbit
( days) around K2-28 (EPIC 206318379), a metal-rich
M4-type dwarf in the Campaign 3 field of the K2 mission. Our follow-up
observations included multi-band transit observations from the optical to the
near infrared, low-resolution spectroscopy, and high-resolution adaptive-optics
(AO) imaging. We perform a global fit to all the observed transits using a
Gaussian process-based method and show that the transit depths in all passbands
adopted for the ground-based transit follow-ups () are within of the K2 value. Based on a model of
the background stellar population and the absence of nearby sources in our AO
imaging, we estimate the probability that a background eclipsing binary could
cause a false positive to be . We also show that K2-28
cannot have a physically associated companion of stellar type later than M4,
based on the measurement of almost identical transit depths in multiple
passbands. There is a low probability for a M4 dwarf companion (), but even if this were the case, the size of K2-28b
falls within the planetary regime. K2-28b has the same radius (within
) and experiences a similar irradiation from its host star as the
well-studied GJ~1214b. Given the relative brightness of K2-28 in the near
infrared ( mag and mag) and relatively deep
transit (), a comparison between the atmospheric properties of these
two planets with future observations would be especially interesting.Comment: 11 pages, 9 figures, accepted to Ap
Multicolor and multi-spot observations of Starlink's Visorsat
This study provides the results of simultaneous multicolor observations for
the first Visorsat (STARLINK-1436) and the ordinary Starlink satellite,
STARLINK-1113 in the , , , , , , , ,
, , , and bands to quantitatively investigate the extent to
which Visorsat reduces its reflected light. Our results are as follows: (1) in
most cases, Virorsat is fainter than STARLINK-1113, and the sunshade on
Visorsat, therefore, contributes to the reduction of the reflected sunlight;
(2) the magnitude at 550 km altitude (normalized magnitude) of both satellites
often reaches the naked-eye limiting magnitude ( 6.0); (3) from a blackbody
radiation model of the reflected flux, the peak of the reflected components of
both satellites is around the band; and (4) the albedo of the near infrared
range is larger than that of the optical range. Under the assumption that
Visorsat and STARLINK-1113 have the same reflectivity, we estimate the covering
factor, , of the sunshade on Visorsat, using the blackbody radiation
model: the covering factor ranges from . From
the multivariable analysis of the solar phase angle (Sun-target-observer), the
normalized magnitude, and the covering factor, the phase angle versus covering
factor distribution presents a moderate anti-correlation between them,
suggesting that the magnitudes of Visorsat depend not only on the phase angle
but also on the orientation of the sunshade along our line of sight. However,
the impact on astronomical observations from Visorsat-designed satellites
remains serious. Thus, new countermeasures are necessary for the Starlink
satellites to further reduce reflected sunlight.Comment: 31 pages, 9 figures, published in PAS