5 research outputs found
Speckle observations of binary stars with a 0.5 m telescope
We present 36 observations of 17 visual binaries of moderate separation
(range from 0.15'' to 0.79'') made with the 50 cm Cassegrain telescope of the
Jagiellonian University in Cracow. The speckle interferometry technique was
combined with modest optical hardware and a standard photometric CCD camera. We
used broad-band V,R,I filters without a Risley prism to reduce differential
colour refraction, so we performed model analysis to investigate the influence
of this effect on the results of measurements. For binary components of
spectral type O-F, the difference of three spectral classes between them should
bias their relative positions by no more than a couple of tens of
milliarcseconds (mas) for moderate zenith distances. The statistical analysis
of our results confirmed this conclusion. A cross-spectrum approach was applied
to resolve the quadrant ambiguity. Our separations have RMS deviations of
0.012'' and our position angles have RMS deviations of 1.8 deg. Relative
photometry in V, R and I filters appeared to be the less accurately determined
parameter. We discuss our errors in detail and compare them to other speckle
data. This comparison clearly shows the high value of our measurements. We also
present an example of the enhancement of image resolution for an extended
object of angular size greater than the atmospheric coherence patch using
speckle interferometry techniques.Comment: Submitted to Astronomy & Astrophysic
Fast Rotation and Trailing Fragments of the Active Asteroid P/2012 F5 (Gibbs)
While having a comet-like appearance, P/2012 F5 (Gibbs) has an orbit native
to the Main Asteroid Belt, and physically is a km-sized asteroid which recently
(mid 2011) experienced an impulsive mass ejection event. Here we report new
observations of this object obtained with the Keck II telescope on UT 2014
August 26. The data show previously undetected 200-m scale fragments of the
main nucleus, and reveal a rapid nucleus spin with a rotation period of 3.24
0.01 hr. The existence of large fragments and the fast nucleus spin are
both consistent with rotational instability and partial disruption of the
object. To date, many fast rotators have been identified among the minor
bodies, which, however, do not eject detectable fragments at the present-day
epoch, and also fragmentation events have been observed, but with no rotation
period measured. P/2012 F5 is unique in that for the first time we detected
fragments and quantified the rotation rate of one and the same object. The
rapid spin rate of P/2012 F5 is very close to the spin rates of two other
active asteroids in the Main Belt, 133P/Elst-Pizarro and (62412), confirming
the existence of a population of fast rotators among these objects. But while
P/2012 F5 shows impulsive ejection of dust and fragments, the mass loss from
133P is prolonged and recurrent. We believe that these two types of activity
observed in the rapidly rotating active asteroids have a common origin in the
rotational instability of the nucleus.Comment: To appear in the 2015 March 20 issue of ApJ Letter
A photometric and spectroscopic study of WW And - an Algol-type, long period binary system with an accretion disc
We have analyzed the available spectra of WW And and for the first time
obtained a reasonably well defined radial velocity curve of the primary star.
Combined with the available radial velocity curve of the secondary component,
these data led to the first determination of the spectroscopic mass ratio of
the system at q-spec = 0.16 +/- 0.03. We also determined the radius of the
accretion disc from analysis of the double-peaked H-alpha emission lines. Our
new, high-precision, Johnson VRI and the previously available Stromgren vby
light curves were modelled with stellar and accretion disc models. A consistent
model for WW And - a semidetached system harbouring an accretion disc which is
optically thick in its inner region, but optically thin in the outer parts -
agrees well with both spectroscopic and photometric data.Comment: Accepted by New Astronom
Rotation State of Comet 103P/Hartley 2 from Radio Spectroscopy at 1 mm
International audienceThe nuclei of active comets emit molecules anisotropically from discrete vents. As the nucleus rotates, we expect to observe periodic variability in the molecular emission line profiles, which can be studied through millimeter/submillimeter spectroscopy. Using this technique we investigated the HCN atmosphere of comet 103P/Hartley 2, the target of NASA's EPOXI mission, which had an exceptionally favorable apparition in late 2010. We detected short-term evolution of the spectral line profile, which was stimulated by the nucleus rotation, and which provides evidence for rapid deceleration and excitation of the rotation state. The measured rate of change in the rotation period is 1.00 ± 0.15 minutes day<SUP>-1</SUP> and the period itself is 18.32 ± 0.03 hr, both applicable at the epoch of the EPOXI encounter. Surprisingly, the spin-down efficiency is lower by two orders of magnitude than the measurement in comet 9P/Tempel 1 and the best theoretical prediction. This secures rotational stability of the comet's nucleus during the next few returns, although we anticipate a catastrophic disruption from spin-up as its ultimate fate