How semiregular are irregular variables?

We investigate the question whether there is a real difference in the light change between stars classified as semiregular (SRV) or irregular (Lb) variables by analysing photometric light curves of 12 representatives of each class. Using Fourier analysis we try to find a periodic signal in each light curve and determine the S/N of this signal. For all stars, independent of their variability class we detect a period above the significance threshold. No difference in the measured S/N between the two classes could be found. We propose that the Lb stars can be seen as an extension of the SRVs towards shorter periods and smaller amplitudes. This is in agreement with findings from other quantities which also showed no marked difference between the two classes (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

How common is the Milky Way–satellite system alignment?

The highly flattened distribution of satellite galaxies in the Milky Way (MW) presents a number of puzzles. First, its polar alignment stands out from the planar alignments commonly found in other galaxies. Secondly, recent proper-motion measurements reveal that the orbital angular momentum of at least three, and possibly as many as eight, of the MW's satellites points (within  30°  ) along the axis of their flattened configuration, suggesting some form of coherent motion. In this paper, we use a high-resolution cosmological simulation to investigate whether this pattern conflicts with the expectations of the cold dark matter model of structure formation. We find that this seemingly unlikely setup occurs often: approximately 35 per cent of the time, we find systems in which the angular momentum of three individual satellites points along, or close to, the short axis of the satellite distribution. In addition, in 30 per cent of the systems we find that the net angular momentum of the six best-aligned satellites lies within  35°  of the short axis of the satellite distribution, as observed for the MW.     

Possible consequences of absence of “jupiters” in planetary systems

The formation of the gas giant planets Jupiter and Saturn probably required the growth of massive 15 Earth-mass cores on a time scale shorter than the 10⁷ time scale for removal of nebular gas. Relatively minor variations in nebular parameters could preclude the growth of full-size gas giants even in systems in which the terrestrial planet region is similar to our own. Systems containing failed Jupiters, resembling Uranus and Neptune in their failure to capture much nebular gas, would be expected to contain more densely populated cometary source regions. They will also eject a smaller number of comets into interstellar space. If systems of this kind were the norm, observation of hyperbolic comets would be unexpected. Monte Carlo calculations of the orbital evolution of region of such systems (the Kuiper belt) indicate that throughout Earth history the cometary impact flux in their terrestrial planet regions would be 1000 times greater than in our Solar System. It may be speculated that this could frustrate the evolution of organisms that observe and seek to understand their planetary system. For this reason our observation of these planets in our Solar System may tell us nothing about the probability of similar gas giants occurring in other planetary systems. This situation can be corrected by observation of an unbiased sample of planetary systems.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

How old are SN Ia progenitor systems? New observational constraints on the distribution of time delays from GALEX

The time delay between the formation of the progenitor systems of Type Ia supernovae (SNe Ia) and their detonation is a vital discriminant between the various progenitor scenarios that have been proposed for them. We use Sloan Digital Sky Survey optical and Galaxy Evolution Explorer ( GALEX ) ultraviolet observations of the early-type host galaxies of 21 nearby SNe Ia and quantify the presence or absence of any young stellar population to constrain the minimum time delay for each supernova. We find that early-type host galaxies lack 'prompt' SNe Ia with time delays of ≲100 Myr and that ∼70 per cent SNe Ia have minimum time delays of 275 Myr–1.25 Gyr, with a median of 650 Myr, while at least 20 per cent SNe Ia have minimum time delays of at least 1 Gyr at 95 per cent confidence and two of these four SNe Ia are likely older than 2 Gyr. The distribution of minimum time delays observed matches most closely the expectation for the single-degenerate channel with a main sequence donor. Furthermore, we do not find any evidence that subluminous SNe Ia are associated with long time delays.     

Fallback in bipolar planetary nebulae?

The subclass of bipolar Planetary Nebulae(PNe)exhibits well-defined low-power outflows and some shows shock-related equatorial spiderweb structures and hourglas...     

UU CNC and VZ PSC,contact systems before the common envelope phase?

We have analyzed the existing photoelectric light curves of twoK-type binary systems: UU Cnc, with a period of about 100 days, and VZ Psc, with a period of about 6 hours. Both show a large overcontact (38% for UU Cnc, 56% for VZ Psc) and a large temperature difference between components (T1500 K and 1100 K, respectively). In the case of VZ Psc, the variability is due only to the non-spherical shape, i.e., no eclipse occurs, but the determination of the photometric solution is made possible by the existence of a spectroscopic mass ratio. We find that UU Cnc is now probably undergoing Case C mass transfer in a dynamical time-scale, with the mass ratio reversal having already occurred; the system is in contact, and is likely to evolve to a 100% filling factor, that is the so-called pre-common envelope phase, a unique case never observed before. The situation for VZ Psc is more uncertain, but a similar, although not identical, possibility exists.Associated with the Istituto Nazionale Fisica Nucleare, Italy.On leave from N. Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw, Poland.     

On possible circumbinary configurations of the planetary systems of α Centauri and EZ Aquarii

Possible configurations of the planetary systems of the binary stars α Cen A–BandEZAqr A–C are analyzed. The P-type orbits—circumbinary ones, i.e., the orbits around both stars of the binary, are studied. The choice of these systems is dictated by the fact that α Cen is closest to us in the Galaxy, while EZ Aqr is the closest system whose circumbinary planets, as it turns out, may reside in the “habitability zone.” The analysis has been performed within the framework of the planar restricted three-body problem. The stability diagrams of circumbinary motion have been constructed: on representative sets of initial data (in the pericentric distance–eccentricity plane), we have computed the Lyapunov spectra of planetary motion and identified the domains of regular and chaotic motion through their statistical analysis. Based on present views of the dynamics and architecture of circumbinary planetary systems, we have determined the most probable planetary orbits to be at the centers of the main resonance cells, at the boundary of the dynamical chaos domain around the parent binary star, which allows the semimajor axes of the orbits to be predicted. In the case of EZ Aqr, the orbit of the circumbinary planet is near the habitability zone and, given that the boundary of this zone is uncertain, may belong to it.     

Pseudo-resonance absorption lines in planetary nebulae: Discovery?

The possibility of the formation of pseudo-resonance absorption lines in planetary nebulae is predicted only theoretically. However, this has not been confirmed by direct observations. In the present article an attempt has been made to show, as a result of careful analysis of IUE spectral recordings for a group of planetary nebulae, that the existence of one pseudo-resonance line 1300 SiIII is without doubt at least in spectra of three planetary nebulae: NGC 2610, NGC 3587, and NGC 6891. The presence of this line in the spectra of the other three planetary nebulae, NGC 6210, IC 3568, and IC 4776, seems to be probable. The role of the interstellar selective absorption, the blending effect by the resonance lines of SiII,Oi, andSi in the formation of the pseudo-resonance line 1300 SiIII as well as the possibility of formation of this line in the photosphere of central star of nebula were analysed.     

Do planetary encounters reset surfaces of near Earth asteroids?

Processes such as the solar wind sputtering and micrometeorite impacts can modify optical properties of surfaces of airless bodies. This explains why spectra of the main belt asteroids, exposed to these ‘space weathering’ processes over eons, do not match the laboratory spectra of ordinary chondrite (OC) meteorites. In contrast, an important fraction of Near Earth Asteroids (NEAs), defined as Q-types in the asteroid taxonomy, display spectral attributes that are a good match to OCs. Here we study the possibility that the Q-type NEAs underwent recent encounters with the terrestrial planets and that the tidal gravity (or other effects) during these encounters exposed fresh OC material on the surface (thus giving it the Q-type spectral properties). We used numerical integrations to determine the statistics of encounters of NEAs to planets. The results were used to calculate the fraction and orbital distribution of Q-type asteroids expected in the model as a function of the space weathering timescale, t_sw (see main text for definition), and maximum distance, r^∗, at which planetary encounters can reset the surface. We found that t_sw ∼ 10⁶ yr (at 1 AU) and r^∗ ∼ 5R_pl, where R_pl is the planetary radius, best fit the data. Values t_sw < 10⁵ yr would require that r^∗ > 20R_pl, which is probably implausible because these very distant encounters should be irrelevant. Also, the fraction of Q-type NEAs would be probably much larger than the one observed if t_sw > 10⁷ yr. We found that t_sw ∝ q², where q is the perihelion distance, expected if the solar wind sputtering controls t_sw, provides a better match to the orbital distribution of Q-type NEAs than models with fixed t_sw. We also discuss how the Earth magnetosphere and radiation effects such as YORP can influence the spectral properties of NEAs.     

How peculiar are GRS 1915+105 and GRO J1655−40?

The X-ray properties of the two galactic microquasars GRS 1915+105 and GRO J1655−40 are rather perculiar. In particular, GRS 1915+105 displays a richness of variability never observed in any other source. Nevertheless, many characteristics of these two sources are not unlike those expected from black-hole candidates on the basis of other known sources. I discuss these similarities and suggest that the connection between these and other more “conventional” systems can potentially lead to a better understanding of accretion around black holes.     

Are extrasolar oceans common throughout the Galaxy?

Light and cold extrasolar planets such as OGLE 2005‐BLG‐390Lb, a 5.5 Earth masses planet detected via microlensing, could be frequent in the Galaxy according to some preliminary results from microlensing experiments. These planets can be frozen rocky‐ or ocean‐planet, situated beyond the snow line and, therefore, beyond the habitable zone of their system. They can nonetheless host a layer of liquid water, heated by radiogenic energy, underneath an ice shell surface for billions of years, before freezing completely. These results suggest that oceans under ice, like those suspected to be present on icy moons in the Solar system, could be a common feature of cold low‐mass extrasolar planets. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

What are solar faculae?

Results are presented of observations of the facula area near the solar disc center. Observations were performed at the German Vacuum Tower Telescope of the Observatorio del Teide (Tenerife) with the simultaneous use of two instruments, i.e., TESOS in the Ba IIλ 455.4 nm line to measure intensity variations in the photosphere and, at the same time, TIP in the Fe I (λλ 1564.3–1565.8 nm) line to measure Stokes parameters. Using the Fourier filtering technique, we separated the convective and wave components of the intensity field. Stokes parameters Fe I λ 1564.8 nm and λ 1565.2 nm were inverted by the SIR inversion code to estimate the magnetic field strength. We found that the contrast of intergranular lines of the facula in the continuum is almost independent of the magnetic field strengh (in the range from 30 to 160 mT). This result casts doubt on the assertion that solar faculae are a cluster of magnetic flux tubes. Most likely, due to the decrease of transparency of the matter in a strong (approximately 1 kilogauss) magnetic field, we can see the hot walls of granules.     

HCGs: stable and rotating systems?

It is shown that the radial velocity dispersion of the elongated HCGs (b/a ≤ 0.2) with smaller two‐dimensional galaxy‐galaxy median projected separation R is, on average, higher than those of the groups with larger R. It shows that galaxies in a group move preferentially along its elongation. Inspection of radial velocities of member galaxies in chain‐like and in roundish HCGs shows that galaxies in HCGs most probably rotate around the gravitational center of the corresponding group. Other two possible mechanisms: flying apart of galaxies from the group in opposite directions, and infall of field galaxies upon the group are excluded. It follows that HCGs are, probably, more stable formations, than it has been assumed. In this case the known inconsistencies between the results of the N‐body simulations and the observational facts are being excluded.     

Mg-rich harzburgites from Vesta: Mantle residua or cumulates from planetary differentiation?

We describe petrographic, electron microprobe, and laser ablation ICP-MS analyses of Mg-rich harzburgite clasts in the Dominion Range 2010 howardites, and conclude that they are xenolithic samples of the vestan mantle. Key chemical and petrologic characteristics of these rocks provide tests for differentiation models. Our results indicate the mantle of Vesta formed through variable degrees of partial melting, which left behind a harzburgite and possibly dunite residuum. The Mg-rich clasts are composed of orthopyroxene and olivine, with minor clinopyroxene, FeNi metal, and distinctive pyroxene–chromite symplectites. We use mineral chemistry to demonstrate the absence of a genetic link between diogenites and the Mg-rich harzburgites. We propose a secondary origin for the formation of symplectites: interaction of silicate and metallic melts during primordial differentiation and core formation. The occurrence of FeNi metal containing ~1.5 wt% Cr within the assemblage indicates a very reducing environment during mantle differentiation (≪IW). Our study suggests that Vesta did not experience complete melting early in its history, and instead supports the formation of a shallow magma ocean.     

Where are the Uranus Trojans?

The area of stable motion for fictitious Trojan asteroids around Uranus’ equilateral equilibrium points is investigated with respect to the inclination of the asteroid’s orbit to determine the size of the regions and their shape. For this task we used the results of extensive numerical integrations of orbits for a grid of initial conditions around the points L ₄ and L ₅, and analyzed the stability of the individual orbits. Our basic dynamical model was the Outer Solar System (Jupiter, Saturn, Uranus and Neptune). We integrated the equations of motion of fictitious Trojans in the vicinity of the stable equilibrium points for selected orbits up to the age of the Solar system of 5 × 10⁹ years. One experiment has been undertaken for cuts through the Lagrange points for fixed values of the inclinations, while the semimajor axes were varied. The extension of the stable region with respect to the initial semimajor axis lies between 19.05 ≤ a ≤ 19.3 AU but depends on the initial inclination. In another run the inclination of the asteroids’ orbit was varied in the range 0° < i < 60° and the semimajor axes were fixed. It turned out that only four ‘windows’ of stable orbits survive: these are the orbits for the initial inclinations 0° < i < 7°, 9° < i < 13°, 31° < i < 36° and 38° < i < 50°. We postulate the existence of at least some Trojans around the Uranus Lagrange points for the stability window at small and also high inclinations.     

Where are the halo stars?

In the usual and most widespread textbook picture of the Milky Way Galaxy, disk stars like the Sun are referred to as Population I, the spheroidal or halo component in turn as Population II. The latter is thought of as the pressure-supported, metal-poor relic of the early Galaxy, with renewed interest in recent years in the search for dark matter via microlensing. Modelling the putative massive compact halo objects however, faces the problem that the stellar halo is generally considered to consist of only a few billion solar masses. Here we present observational evidence that even this low budget may be a factor ten too high. If so, this immediately implies that the classical population II of halo stars is fairly irrelevant, not only in the dark matter context, but, in particular, in models of the formation and evolution of the Milky Way Galaxy.     

How Linear Are Typical CCDs?

The typical linearity achievable with CCDs was questioned at the previous ESO Optical Detector Workshop in 1993. This paper describes the efforts at CTIO since then to develop a technique for measuring linearity accurately, and rapidly enough to make the exploration of CCD operating parameters practical. A simple circuit has been adopted which stabilizes the intensity of a pulsed LED. It is compact enough to be installed behind the shutter so that linearity can be monitored at the telescope while the dome lights are on. Methods are described for verifying the linearity and stability of the measurement system itself. These requirements are very stringent, since CCD gain variations have typically been measured to be 0.2% or less over most of the operating range. Methods are proposed for reducing non-linearity further, and for generating each new linearity curve from a single exposure, after having taken several calibration exposures. Several discrepancies have been seen between linearity of point sources and linearity measured with flat illumination: the amplitudes were similar but the gain variations had opposite slopes over the central part of the curve, and a more pronounced signal deficit has been noted at low light levels for point sources, which is equivalent to the subtraction of few electrons from every pixel.     

Proper elements: What are they?

The general ideas about the calculation of proper elements are given here, followed by a comparison of the hypotheses and simplifications made in three different theories: YKM theory, composition of the contributions of Yuasa, Kneevi and Milani, W theory corresponding to Williams's work and HLM theory, paper of Lemaitre and Morbidelli, based on Henrard's semi numerical method. Some short numerical comparisons conclude the paper.     

Where are the rings of Neptune?

Stable rings can exist at inclinations of 0–15°, 165°–180°, or ～90° to Neptune's equator, but perturbations due to the massive satellite Triton would produce a severe “warping” of the ring plane. If Neptune possesses rings, they may not lie in the plane of its equator.