The luminosity-redshift relation in brane-worlds: I. Analytical results

The luminosity distance - redshift relation is analytically given for generalized Randall-Sundrum type II brane-world models containing dark radiation. The derived expressions contain both elementary functions and elliptic integrals of the first and second kind. First we derive the relation for models with the Randall-Sundrum fine-tuning. Then we generalize the method for models with cosmological constant. The analytical results are suitable for testing brane-world models when future supernova data at higher redshifts will be available.Comment: v2: Improved discussion and new references; analytical results kept, comparison with observation moved to astro-ph/0702610, 18 pages, 2 figures v3: Minor improvements, few new references. Version to appear in the initial issue of PMC Physics

Explaining the elongated shape of 'Oumuamua by the Eikonal abrasion model

The photometry of the minor body with extrasolar origin (1I/2017 U1) 'Oumuamua revealed an unprecedented shape: Meech et al. (2017) reported a shape elongation b/a close to 1/10, which calls for theoretical explanation. Here we show that the abrasion of a primordial asteroid by a huge number of tiny particles ultimately leads to such elongated shape. The model (called the Eikonal equation) predicting this outcome was already suggested in Domokos et al. (2009) to play an important role in the evolution of asteroid shapes.Comment: Accepted by the Research Notes of the AA

Advantages of unocculted optical systems in lucky imaging

Lucky imaging is a competitive alternative for high-resolution imaging with a possibility of applications on small telescopes. The advantage of this technique is that small telescopes are not time expensive, therefore long observing runs, lasting for several hours or nights can be planned, enabling for time-resolved observation of sources in crowded fields. In the ideal case, a lucky image is diffraction-limited, while the actual resolution (in the order of several 0.1 arc seconds) is still close to the diffraction-limit of small telescopes. However, occulted optical systems, such as Cassegrain or RCC (Ritchey-Chretien-Coude) perform a poor imaging near the diffraction limit, because the secondary mirror significantly decreases the contrast. By basic optical calculations one can conclude that a typical Cassegrain-system has similar PSF to that of an unocculted telescope with a 40% less aperture, while the Strehl ratio is decreased to about 30% simply due to the secondary mirror. Since the profile is widened and the precious signal decreases significantly, a well-constructed unocculted telescope can perform at least as well as a Cassegrain system which is twice as large. My conclusion is therefore that "dropping out the secondary mirror makes the aperture double" — at least in Lucky Imaging applications

The power of wavelets in analysis of transit and phase curves in presence of stellar variability and instrumental noise III. Accuracy of transit parameters

Correlated noise in exoplanet light curves, such as noises from stellar activity, convection noise, and instrumental noises distorts the exoplanet transit light curves, and leads to biases in the best-fit transit parameters. An optimal fitting algorithm is stable against the presence of correlated noises and lead to statistically consistent results, i.e. the actual biases are usually within the error interval. This is not automatically satisfied by most of the algorithms in everyday use, and the testing of the algorithms is necessary. In this paper, we describe a bootstrapping-like test to handle with the general case, and apply this to the wavelet-based TLCM (Transit and Light Curve Modeller) algorithm, testing it for the stability against the correlated noise. We contrast the results to the FITSH algorithm that is based on a white noise assumption. We simulated transit light curves with previously known parameters in the presence of a correlated noise model generated by an ARIMA (Autoregressive Integretad Moving Average) process. Then we solved the simulated observations, and examined the resulting parameters and error intervals. We have found that the assumption of FITSH that only white noise is present led to inconsistencies in the results: the distribution of best-fit parameters is by a factor of 3--6 broader then the determined error intervals. On the other hand, the wavelet-based TLCM algorithm handles the correlated noise properly, leading to properly determined parameter and error intervals which are perfectly consistent with the actual biases.Comment: Submitted to A&A, favorable referee report received, 11 pages, 8 figure

Large size and slow rotation of the trans-Neptunian object (225088) 2007 OR10 discovered from Herschel and K2 observations

We present the first comprehensive thermal and rotational analysis of the second most distant trans-Neptunian object (225088) 2007 OR10. We combined optical light curves provided by the Kepler space telescope -- K2 extended mission and thermal infrared data provided by the Herschel Space Observatory. We found that (225088) 2007 OR10 is likely to be larger and darker than derived by earlier studies: we obtained a diameter of d=1535^{+75}_{-225} km which places (225088) 2007 OR10 in the biggest top three trans-Neptunian objects. The corresponding visual geometric albedo is p_V=0.089^{+0.031}_{-0.009}. The light curve analysis revealed a slow rotation rate of P_rot=44.81+/-0.37 h, superseded by a very few objects only. The most likely light-curve solution is double-peaked with a slight asymmetry, however, we cannot safely rule out the possibility of having a rotation period of P_rot=22.40+/-0.18 h which corresponds to a single-peaked solution. Due to the size and slow rotation, the shape of the object should be a MacLaurin ellipsoid, so the light variation should be caused by surface inhomogeneities. Its newly derived larger diameter also implies larger surface gravity and a more likely retention of volatiles -- CH_4, CO and N_2 -- on the surface.Comment: Accepted for publication in AJ, 8 pages in emulateapj styl

Rotational Properties of Hilda Asteroids Observed by the K2 Mission

Hilda asteroids orbit at the outer edge, or just outside of the Main Belt, occupying the 2:3 mean motion resonance with Jupiter. It is known that the group shows a mixed taxonomy that suggests the mixed origin of Hilda members, having migrated to the current orbit both from the outer Main Belt and from the Trojans swarms. But there are still few observations for comparative studies that help in understanding the Hilda group in deeper details. We identified 125 individual light curves of Hilda asteroids observed by the K2 mission. We found that despite of the mixed taxonomies, the Hilda group highly resembles to the Trojans in the distribution of rotation periods and amplitudes, and even the LR group (mostly C and X-type) Hildas follow this rule. Contrary to the Main Belt, Hilda group lacks the very fast rotators. The ratio of extremely slow rotators (P>100 h) is a surprising 18%, which is unique in the Solar System. The occurrence rate of asteroids with multiple periods (4%) and asteroids with three maxima in the light curves (5%) can be signs of high rate of binarity, which we can estimate as 25% within the Hilda group

Ancillary science with Ariel: Feasibility and scientific potential of young stellar object observations

To investigate the feasibility of ancillary target observations with ESA's Ariel mission, we compiled a list of potentially interesting young stars: FUors, systems harbouring extreme debris discs and a larger sample of young stellar objects showing strong near/mid-infrared excess. These objects can be observed as additional targets in the waiting times between the scheduled exoplanet transit and occultation observations. After analyzing the schedule for Ariel an algorithm was constructed to find the optimal target to be observed in each gap. The selection was mainly based on the slew and stabilization time needed to observe the selected YSO, but it also incorporated the scientific importance of the targets and whether they have already been sufficiently measured. After acquiring an adequately large sample of simulation data, it was concluded that approximately 99.2% of the available -- at least one hour long -- gaps could be used effectively. With an average slewing and stabilization time of about 16.7 minutes between scheduled exoplanet transits and ancillary targets, this corresponds to an additional $2881 \pm 56$ hours of active data gathering. When this additional time is used to observe our selected 200 ancillary targets, a typical signal-to-noise ratio of $\sim$10$^4$ can be achieved along the whole spectral window covered by Ariel.Comment: Accepted for publication in Experimental Astronom