3,467 research outputs found
Pushing the limits: K2 observations of the trans-Neptunian objects 2002 GV31 and (278361) 2007 JJ43
We present the first photometric observations of trans-Neptunian objects
(TNOs) taken with the Kepler space telescope, obtained in the course of the K2
ecliptic survey. Two faint objects have been monitored in specifically designed
pixel masks that were centered on the stationary points of the objects, when
their daily motion was the slowest. In the design of the experiment, only the
apparent path of these objects were retrieved from the detectors, i.e. the
costs in terms of Kepler pixels were minimized. Because of the faintness of the
targets we employ specific reduction techniques and co-added images. We measure
rotational periods and amplitudes in the unfiltered Kepler band as follows: for
(278361) 2007 JJ43 and 2002 GV31 we get P_rot=12.097 h and P_rot=29.2 h while
0.10 and 0.35 mag for the total amplitudes, respectively. Future space
missions, like TESS and PLATO are not well suited to this kind of observations.
Therefore, we encourage to include the brightest TNOs around their stationary
points in each observing campaign to exploit this unique capability of the K2
Mission -- and therefore to provide unbiased rotational, shape and albedo
characteristics of many objects.Comment: Accepted for publication in ApJ Letters, 5.2 pages in emulateapj
style, misspelled 2007 JJ43 designation correcte
Frozen to death? -- Detection of comet Hale-Bopp at 30.7 AU
Comet Hale--Bopp (C/1995 O1) has been the single most significant comet
encountered by modern astronomy, still having displayed significant activity at
25.7 AU solar distance in late 2007. It is a puzzling question when and where
this activity will finally cease. Here we present new observations with the ESO
2.2m telescope at La Silla to check the activity of Hale--Bopp at 30.7 AU solar
distance. On 2010-12-04, 26 CCD images were taken with 180 s exposure times for
photometry and morphology. The comet was detected in R and had a total
brightness of 23.3+-0.2 mag, referring to an absolute brightness of
R(1,1,0)=8.3. The profile of the coma was star-like at a seeing of 1.9",
without any evidence of a coma or tail extending farther than 2.5" (=55,000 km
in projection) and exceeding 26.5 mag/arcs^2 surface brightness. The measured
total brightness corresponds to a relative total reflecting surface, a_RC, of
485 km^2, nine times less than three years before. The calculated a_RC value
would imply a nucleus with 60--65 km radius assuming 4% albedo. This size
estimate is in significant contradiction with the previous results scattering
around 35 km. Therefore we suggest that the comet may still be in a low-level
activity, despite the lack of a prominent coma. Alternatively, if the nucleus
is already dormant, the albedo should be as high as 13%, assuming a radius of
35 km. With this observation, Hale--Bopp has been the most distant comet ever
observed, far beyond the orbit of Neptune.Comment: 4 pages, accepted by A&
Main-Belt Asteroids in the K2 Engineering Field of View
Unlike NASA's original Kepler Discovery Mission, the renewed K2 Mission will
stare at the plane of the Ecliptic, observing each field for approximately 75
days. This will bring new opportunities and challenges, in particular the
presence of a large number of main-belt asteroids that will contaminate the
photometry. The large pixel size makes K2 data susceptible to the effect of
apparent minor planet encounters. Here we investigate the effects of asteroid
encounters on photometric precision using a sub-sample of the K2 Engineering
data taken in February, 2014. We show examples of asteroid contamination to
facilitate their recognition and distinguish these events from other error
sources. We conclude that main-belt asteroids will have considerable effects on
K2 photometry of a large number of photometric targets during the Mission, that
will have to be taken into account. These results will be readily applicable
for future space photometric missions applying large-format CCDs, such as TESS
and PLATO.Comment: accepted for publication in AJ, 6 page
Mapping a star with transits: orbit precession effects in the Kepler-13 system
Kepler-13b (KOI-13.01) is a most intriguing exoplanet system due to the rapid
precession rate, exhibiting several exotic phenomena. We analyzed
Short Cadence data up to Quarter 14, with a total time-span of 928 days, to
reveal changes in transit duration, depth, asymmetry, and identify the possible
signals of stellar rotation and low-level activity. We investigated long-term
variations of transit light curves, testing for duration, peak depth and
asymmetry. We also performed cluster analysis on quarters. We computed
the autocorrelation function of the out-of-transit light variations. Transit
duration, peak depth, and asymmetry evolve slowly, due to the slowly drifting
transit path through the stellar disk. The detected transit shapes will map the
stellar surface on the time scale of decades. We found a very significant
clustering pattern with 3-orbit period. Its source is very probably the
rotating stellar surface, in the 5:3 spin-orbit resonance reported in a
previous study. The autocorrelation function of the out-of-transit light
variations, filtered to 25.4 hours and harmonics, shows slow variations and a
peak around 300--360 day period, which could be related to the activity cycle
of the host star.Comment: 7 pages, 7 figures, accepted in MNRA
Metal-rich or misclassified? The case of four RR Lyrae stars
We analysed the light curve of four, apparently extremely metal-rich
fundamental-mode RR Lyrae stars. We identified two stars, MT Tel and ASAS
J091803-3022.6 as RRc (first-overtone) pulsators that were misclassified as
RRab ones in the ASAS survey. In the case of the other two stars, V397 Gem and
ASAS J075127-4136.3, we could not decide conclusively, as they are outliers in
the period-Fourier-coefficient space from the loci of both classes, but their
photometric metallicities also favour the RRc classification.Comment: 5 pages, 2 figures, published in IBVS:
http://ibvs.konkoly.hu/cgi-bin/IBVS?617
Constraining RRc candidates using SDSS colours
The light variations of first-overtone RR Lyrae stars and contact eclipsing
binaries can be difficult to distinguish. The Catalina Periodic Variable Star
catalog contains several misclassified objects, despite the classification
efforts by Drake et al. (2014). They used metallicity and surface gravity
derived from spectroscopic data (from the SDSS database) to rule out binaries.
Our aim is to further constrain the catalog using SDSS colours to estimate
physical parameters for stars that did not have spectroscopic data.Comment: 2 pages, 1 figure, proceedings of the RRL2015 - High-Precision
Studies of RR Lyrae Stars conference, to appear in the Communications from
the Konkoly Observator
A modulated RRd star observed by K2
We report the analysis of the double-mode RR Lyrae star EPIC 205209951, the
first modulated RRd star observed from space. The amplitude and phase
modulation are present in both modes.Comment: 2 pages, 3 figures, proceedings of the Joint
TASC2-KASC9-SPACEINN-HELAS8 Conference "Seismology of the Sun and the Distant
Stars 2016", to be published in EPJ Wo
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