Search for circum‐planetary material and orbital period variations of short‐period Kepler exoplanet candidates

A unique short‐period (P = 0.65356(1) d) Mercury‐size Kepler exoplanet candidate KIC012557548b has been discovered recently by Rappaport et al. (2012). This object is a transiting disintegrating exoplanet with a circum‐planetary material–comet‐like tail. Close‐in exoplanets, like KIC012557548b, are subjected to the greatest planet‐star interactions. This interaction may have various forms. In certain cases it may cause formation of the comet‐like tail. Strong interaction with the host star, and/or presence of an additional planet may lead to variations in the orbital period of the planet. Our main aim is to search for comet‐like tails similar to KIC012557548b and for long‐term orbital period variations. We are curious about frequency of comet‐like tail formation among short‐period Kepler exoplanet candidates. We concentrate on a sample of 20 close‐in candidates with a period similar to KIC012557548b from the Kepler mission. We first improved the preliminary orbital periods and obtained the transit light curves. Subsequently we searched for the signatures of a circum‐planetary material in these light curves. For this purpose the final transit light curve of each planet was fitted with a theoretical light curve, and the residuals were examined for abnormalities. We then searched for possible long‐term changes of the orbital periods using the method of phase dispersion minimization. In 8 cases out of 20 we found some interesting peculiarities, but none of the exoplanet candidates showed signs of a comet‐like tail. It seems that the frequency of comet‐like tail formation among short‐period Kepler exoplanet candidates is very low. We searched for comet‐like tails based on the period criterion. Based on our results we can conclude that the short‐period criterion is not enough to cause comet‐like tail formation. This result is in agreement with the theory of the thermal wind and planet evaporation (Perez‐Becker & Chiang 2013). We also found 3 cases of candidates which showed some changes of the orbital period. Based on our results we can see that orbital period changes are not caused by comet‐like tail disintegration processes, but rather by possible massive outer companions. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Physical properties of three short period close binaries:KIC 2715417,KIC 6050116 and KIC 6287172

We present the physical parameters of three short period close binaries using data observed from the Kepler Space Telescope. All of these observations were taken in a single bandpass(which approximates the Johnson V-band). Our three systems are KIC 2715417, KIC 6050116 and KIC 6287172. The first system, KIC 2715417, is considered a semi-detached system with the secondary component filling its Roche lobe. The second system, KIC 6050116, is an overcontact system, while the third system, KIC 6287172, belongs to ellipsoidal variables as deduced from the Roche lobe geometry. For photometric analysis, we used the PHOEBE software package, which is based on the Wilson-Devinney code. Due to lack of spectroscopic data, the photometric mass ratios are determined from the analyses of light curves using the q-search method. The absolute parameters are determined using three different methods(Harmanec, Maceroni Van'tVeer and Gazeas Niarchos).     

KIC 8263801: A clump star in the Kepler open cluster NGC 6866 field?

In this paper we study the field of Kepler open cluster NGC 6866 using the data obtained from Kepler mission collected for a period of 4 years. We search for the red clump (RC) stars amongst the red giant (RG) stars showing solar-like oscillations using median gravity-mode period spacings (ΔP). We find a RG star KIC 8263801 having median gravity-mode period spacing 173.7 ± 6.4 s. We claim based on the median gravity-mode period spacing that KIC 8263801 is a secondary red clump (SRC) star which is massive enough to have ignited Helium burning in a non degenerate core. In the literature, no classification for KIC 8263801 has been provided. This is the first time that a star located in the field of NGC 6866 is classified in this manner.     

Cover Picture: Astron. Nachr. 10/2014

Transit light curve of KIC012557548b which is best represented by an exoplanet with a comet‐like tail (see Z. Garai et al., this issue, p. 1018). (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometric study of five kepler contact binaries

A lot of data in time domain were obtained by the Kepler mission, including many contact binaries. Long-term observation lets us obtain more information about the short time scale variation in their light curves or in their orbital periods. Unfortunately, the exposure time is too long (most of them are 30 minutes). Hence, many variations in light curves are smoothed. To avoid this problem, we analyzed some Kepler contact systems with both long-cadence mode and short-cadence mode data. Using the latest version of the Wilson-Devinney code, we obtained the physical parameters of a batch of contact binaries and find out four targets(KIC 5123176, KIC 5296877, KIC 8496820, KIC 9776718) have low mass ratios (q  <  0.25) and one target (KIC 7950962) has a mass ratio very close to unit.     

Spot and Facula Activity Variations of the Eccentric Detached Eclipsing Binary KIC 8098300 Based on the Time-series Orbital Solutions

The LAMOST spectra and Kepler light curves are combined to investigate the detached eclipsing binary KIC 8098300,which shows the O'Connell effect caused by spot...     

Extragalactic background light absorption signal in the TeV γ-ray spectra of blazars

Recent observations of the TeV γ-ray spectra of the two closest active galactic nuclei (AGNs), Markarian 501 (Mrk 501) and Markarian 421 (Mrk 421), by the Whipple and HEGRA collaborations have stimulated efforts to estimate or limit the spectral energy density (SED) of extragalactic background light (EBL) which causes attenuation of TeV photons via pair-production when they travel cosmological distances. In spite of the lack of any distinct cutoff-like feature in the spectra of Mrk 501 and Mrk 421 (in the interval 0.26–10 TeV) which could clearly indicate the presence of such a photon absorption mechanism, we demonstrate that a strong EBL attenuation signal (survival probability of 10 TeV photon <10⁻²) may still be present in the spectra of these AGNs. This attenuation could escape detection due to ambiguity of spectra interpretation between intrinsic properties of the sources and absorption by EBL. By estimating the minimal and maximal opacity of the universe to TeV γ-ray photons, we calculate the visibility range for current and future γ-ray observatories, and show that the Whipple γ-ray telescope should be able to detect (in 10 hours at a 5σ confidence level) a BL Lac object with properties similar to Mrk 501 during its peak activity located at distances up to z=0.12. The proposed atmospheric Cherenkov telescope array VERITAS should be able to see such an object at least as far as z=0.3. Finally, we show that the proposed experiments, VERITAS, HESS, and MAGIC, may even be able to actually measure the EBL SED because their observations extend to the critical 75–150 GeV regime. In this transition region a distinct “knee-like” feature should exist in the spectra of blazars, which is invariant with respect to their intrinsic properties. The change of the spectral index and flux amplitude across this knee, if observed for several blazars, will provide missing pieces of information needed to measure EBL in the wavelength range 0.1–30 μm.     

On the nature of the Galactic nebula We 1–12

In 1977, Weinberger published a list of 12 new extended possible planetary nebulae (PNe). Whereas, because of their characteristic morphology and/or the presence of a blue central star, almost all of them could easily be suspected to be genuine planetary nebulae, one object (No. 12) captivated because of its unusually bright central star. This find prompted Kaler & Feibelman to question the PN nature of this object (We 1–12) on the basis of IUE spectra. A definite conclusion could, however, not be drawn by them; thus, until now, the real nature of We 1–12 remained unsolved. For the first time, a spectral investigation of both the central star and the nebula is presented in this paper. It definitely shows that this intriguing object is an (isolated) H  ii region and its central star, as previously assumed, is an early B star which serves as the ionizing source. We 1–12, a part of which is coincident with a weak IRAS point source, is at a distance of 2–2.6 kpc and is reddened by E ( B − V )=0.6–0.8 mag.     

Relationship between low and high frequencies in the δ Scuti star KIC 9764965

Two years of Kepler spacecraft data of the δ Sct/γ Dor star KIC 9764965 revealed 67 statistically significant frequencies from 0.45 to 59.17 c d^–1 (0.005 to 0.685 mHz). The 19 low frequencies do not show equidistant period spacing predicted for gravity modes of successive radial order. We note a favored frequency spacing of 2.053 c d^–1 that appears in both the low‐frequency (gravity mode) region and high‐frequency (pressure mode) regions. The value of this frequency spacing also occurs as a dominant low frequency and in a high‐frequency triplet. A peak at exactly twice the value of the 2.053 cd^–1 mode is shown not to be a Fourier harmonic of the low‐frequency peak due to a different amplitude variability. This behavior is also seen in other δ Sct stars. The test for resonant mode coupling between low and high frequencies could not be carried out due to the small amplitudes of the peaks, making it difficult to separate the parent and child modes. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analytic solutions to the accretion of a rotating finite cloud towards a central object – I. Newtonian approach

We construct a steady analytic accretion flow model for a finite rotating gas cloud that accretes material to a central gravitational object. The pressure gradients of the flow are considered to be negligible, and so the flow is ballistic. We also assume a steady flow and consider the particles at the boundary of the spherical cloud to be rotating as a rigid body, with a fixed amount of inwards radial velocity. This represents a generalization to the traditional infinite gas cloud model described by Ulrich. We show that the streamlines and density profiles obtained deviate largely from the ones calculated by Ulrich. The extra freedom in the choice of the parameters on the model can naturally account for the study of protostars formed in dense clusters by triggered mechanisms, where a wide variety of external physical mechanisms determine the boundary conditions. Also, as expected, the model predicts the formation of an equatorial accretion disc about the central object with a radius different from the one calculated by Ulrich.     

KIC 7732964 – A Possible Candidate FK Com-Type Star

Astrophysics - This article is a brief survey of our previous work devoted to searching for candidate type FK Com giant stars and an analysis of data for yet another new candidate, KIC 7732964....     

Formation of the binary near‐Earth object 1996 FG3: Can binary NEOs be the source of short‐CRE meteorites?

Abstract— 1996 FG₃ is a binary near‐Earth object (NEO) that was likely formed during a tidal disruption event. Our results indicate that the formation of this binary object was unlikely to have occurred when the progenitor had a encounter velocity with the Earth significantly smaller than its current value (10.7 km/s); The formation of the binary object on an orbit similar to the present one is possible, and the survival of the satellite constrains this to have happened less than 1.6 Ma ago. However, the binary object could also have been formed when the progenitor's encounter velocity with Earth was >12 km/s, and in this case we cannot constrain its formation age. Our results indicate that tidal disruptions occurring among NEOs with low velocity encounters with Earth are unlikely to produce long‐lasting NEO binaries. Thus, tidal disruption may not be able to completely re‐supply the observed population. This would imply that a significant fraction of the observed NEO binaries evolved out of the main asteroid belt. Overall, our results suggest to us that the CM2 meteorites having cosmic ray exposure (CRE) ages of ?200,000 yr were likely liberated by the tidal disruption of a primitive NEO with a relative velocity with the Earth significantly smaller than that of 1996 FG₃. We propose a list of such objects, although as far as we know, none of the candidates is a binary for the reasons described above.     

Stability of frosts in the solar system

Calculations on the stability of various frosts (against evaporation) for solar system objects in circular and elliptical orbits are made. It is found that the stability of these frosts is dependent on the rate of rotation of the object, the latitude of the area on the object being considered, and the eccentricity of the orbit as well as its mean distance from the Sun. These factors greatly influence the amount of solar radiation incident and reradiated from a given area on the object. The likelihood of finding these frosts on the surfaces of objects and the lifetimes of objects composed of these frosts is discussed.     

Possible evidence for the existence of an H II region around the neutron star in LSI+65°010

Our spectroscopic observation of the Be/X-ray binary LSI+65°010 showed a dramatic variation in November 1992 with an increase by a factor of more than 3 in the equivalent width of the H_α emission line. This supports the view that the primary is a Be star rather than a supergiant. A well-defined double-peaked profile in seen in the spectrum of September 1994: while the red peak remained at 6563 Å, the blue one was −7.2Å to the blue. We suggest that such a profile is caused by the superposition of two emission lines, one from the shell of the Be star, one from an H II region around the neutron star. This provides, for the first time, direct observational evidence for the existence of a H II region around compact object and caused by X-ray emission. On 1992-11-04, the red side of the H_α line did not change while the blue side was greatly enhanced. We suggest that this may be caused by the H II region around the neutron star.     

On the hypothesis of the genetic connection of comets with Pluto and the transneptunian object 2003 UB 313

The hypothesis suggested by Guliev on transneptunian objects as sources of comets is considered. The motion equations for 137 near-parabolic comets over a time interval of 5000 years were numerically integrated. No interaction between 78 comets and the transneptunian object 2003 UB 313 has been revealed: the comets were farther than 3 AU from it. It has been shown that 59 comets—candidates to Pluto’s family-approached Pluto at a distance larger than 0.7 AU. The fulfilled analysis allows us to conclude that Guliev’s hypothesis on transneptunian objects as sources of comets is groundless.     

Regularity of Extrasolar Planetary Systems and the Role of the Star Metallicity in the Formation of Planets (Review)

The discovery in 1995 of the first extrasolar giant planet 51 Peg b initiated the physics of extrasolar planetary systems. By May 2004, the total number of the detected planets orbiting other stars was 122, including 24 hot jupiters, which have a semimajor axis of the orbit of less than 0.15 AU. Due to the high activity of researchers who work with the radial-velocity method, the probable candidates, say, in the 75-parsec radius, are quickly exhausted. The OGLE-type objects, even if their number increases, may only slightly contribute to the physics of extrasolar planets (or exoplanets), because even to determine the type of the companion (a giant planet, brown dwarf, or star of small mass) is extremely problematic for such weak objects. A search for Earth-like planets is still far beyond the technical capabilities: the Keplerian velocity of the Sun induced by the Earth is only 0.09 m/s, which requires to improve the results obtained by a factor of 20–30. Particularly important results were obtained in the observations of transits of the object HD 209458b, which became the only object of this type namely due to transits. The hope of finding another short-period object with similar transits is becoming less and less. The important role of the star metallicity in the formation of planetary systems predicted during the first years after the discovery of exoplanets has gained recognition and been developed successfully. Metallicity has become an indicator of the possible presence of planetary systems and, probably, even determines the type of planets. This review also considers the statistical data on the orbital and mass characteristics of exoplanets.     

Variability of η Carinae – III

Spectra (1951–78) of the central object in η Car, taken by A. D. Thackeray, reveal three previously unrecorded epochs of low excitation. Since 1948, at least, these states have occurred regularly in the 2020-d cycle proposed by Damineli et al. They last about 10 per cent of each cycle. Early slit spectra (1899–1919) suggest that at that time the object was always in a low state. JHKL photometry is reported for the period 1994–2000. This shows that the secular increase in brightness found in 1972–94 has continued and its rate has increased at the shorter wavelengths. Modulation of the infrared brightness in a period near 2020 d continues. There is a dip in the JHKL light curves near 1998.0, coincident with a dip in the X-ray light curve. Evidence is given that this dip in the infrared repeats in the 2020-d cycle. As suggested by Whitelock & Laney, the dip is best interpreted as an eclipse phenomenon in an interacting binary system; the object eclipsed being a bright region ('hotspot'), possibly on a circumstellar disc or produced by interacting stellar winds. The eclipse coincides in phase and duration with the state of low excitation. It is presumably caused by a plasma column and/or by one of the stars in the system.     

Light curve solutions of the eclipsing Kepler binaries KIC 5080652, KIC 5285607, KIC 9236858 and KIC 11975363

We carried out light curve solutions of four detached binaries with circular orbits, observed by Kepler. As a result their orbital inclinations, temperatures and relative stellar radii were determined. We estimated also their global parameters on the base of the obtained solutions and empirical relation “temperature, luminosity” for MS stars. The out-of-eclipse light curves of KIC 5080652, KIC 9236858 and KIC 11975363 reveal a trend the bigger amplitudes to correspond to single-waved shape while the two-waved shape to be inherent to the smaller amplitudes. This type of variability was attributed to gradually transition between state with two almost opposite cool spots and state with bigger in size polar spot. We detected also several microflares of KIC 11975363 with amplitudes of 0.002–0.003 mag.     

Modeling KIC 10684673 as a delta Scuti-type variable

KIC 10684673 (TYC 3562-805-1) was observed by the Kepler mission, which obtained nearly 50,000 data points in the short cadence mode from May through June of 2009 for a total of about 33 days. It has been added to the Kepler Eclipsing Binary Catalog as an eclipsing binary. However it is flagged as uncertain in nature. Upon visual inspection, it is found the light curve is not consistent with features present in light curves from typical eclipsing binary systems. Instead, it shows features more consistent with pulsation. In the present study, it is shown the light curve can be satisfactorily modeled by considering the target as single, multi-modal δ Scuti pulsator.