1. The data. We study detailed star formation histories (SFH) of 14 dwarf galaxies in the central parts (≤ 300 Kpc) of the two nearby galaxy groups: M 81 (D=3.6 Mpc) and Cen A (D = 3.8 Mpc). The images of 7 galaxies were selected from the sample of about 50 nearby dwarf galaxies observed with the Advanced Camera for Surveys (ACS) at the Hubble Space Telescope within our prog. 9771 & 10235, (PI I.Karachentsev). The rest of the images (ACS and WFPC2) were taken from the Hubble Archive (prog. 9884, 5898 and 6964).

Preliminary results of the study of the X-ray spectral variability of 12 Narrow Line Seyfert 1 (NLS1) galaxies are presented. Rms spectra are calculated and compared for the whole sample to search for possible variations with black hole mass. A larger sample of AGN is under investigation.

How clumpy are galactic halos? Recent observations around both the Milky Way and the Andromeda galaxy (M31) have revealed numerous faint stellar streams and dwarf galaxies, leading to the belief that more of these may yet remain undetected. In this contribution, we present the map produced from the Megacam/CFHT survey that our group has undertaken in the outer halo of M31 and that, for the first time, gives a deep panoramic view of a significant region of the outer halo of a spiral galaxy. This panoramic survey, which covers ∼ 60 sq. deg. of the southern quadrant of the M31 halo, extends the WFC/INT survey of the inner halo (Ferguson et al. 2002) from a projected distance of ∼ 50 to ∼ 150 kpc. It is deep enough to cover three magnitudes below the tip of the red giant branch of stellar populations at the distance of M31. The survey reveals:

• • Three faint dwarf galaxies with absolute magnitudes in the range -7.3 < M_V < -6.4 and the most remote M31 globular cluster at a projected distance of ∼ 120 kpc from M31 (see Martin et al. 2006 for more details).

• • That the giant stream of Ibata et al. (2001) covers a much wider area than previously expected from shallower surveys, has an apocenter at 125±25 kpc from M31 and is probably due to the accretion of a small disk galaxy.

• • A new stellar stream or shell approximately perpendicular to the minor axis of M31 at a projected distance of 120 kpc and with a metallicity of [Fe/H] ∼ -1.5 (assuming it is at the distance of M31).

• • A new stellar stream along the ma jor axis of M31 that extends to at least 100 kpc from M31 with [Fe/H] ∼ -1.3 (once again assuming it is at the distance of M31).

• • Regions void of any stellar structure brighter than 34-35 mag/arcsec2 at a distance of 100 to 130 kpc from M31.

The survey shows that the outer halo of the Andromeda galaxy is very structured, in qualitative agreement with recent cosmological simulations (e.g. Bullock & Johnston, 2005).

Carignan et al. (C06, 2006, ApJ, 641, L109) recently presented an extended HI rotation curve (RC) of M31, using single dish observations from the 100m Effelsberg and Green Bank telescopes. These data were obtained along the semi-major axis of the approaching half of the M31 HI disk and showed a flat RC at large radius, which extends up to ~35 kpc (using D = 780 kpc). The kinematical analysis of M31 is pursued here and new deep 21cm observations obtained at the Dominion Radio Astrophysical Observatory (DRAO) are presented. A tilted-ring model is fitted to a new HI velocity field, allowing the derivation of the position angle P.A. and inclination i as a function of radius. We concentrate on the approaching half of the disk in order to compare our new results with those from C06. It is shown that the disk warping of M31 does not severely contaminate the kinematics of the neutral gas. As a consequence, the RC from C06 is in very good agreement with the new derived RC.

We present a statistical investigation of shear motion of the EUV footpoints in two-ribbon solar flares, using the high spatial resolution data obtained in 1998–2005 by the Transition Region and Coronal Explorer (TRACE). In this study we have selected 50 well-observed X- and M- class two-ribbon flares. Our preliminary results are: a) 86% (43 out of 50) of these flares show shear change of footpoints and ribbon separation; b) there is no obvious ribbon separation in those 7 flares which have no shear change of the conjugate footpoints; c) in most events, the cessation of shear change is 0–2 minutes earlier than the end of the impulsive phase.

Results of the Stardust mission to sample dust from comet Wild 2 are summarized.

We present total element abundances based upon newly acquired spectrophotometry of a sample of $>$120 Galactic PNe. We continue to explore the use of the near-IR [S III] features to determine S$^{+2}$ abundances and to improve total extrapolated sulfur - a useful metallicity tracer. With this compilation we explore abundance patterns in PNe that reveal signatures of stellar evolution and nucleosynthesis as well as larger-scale galactic chemical evolution.

Eta Carinae (ηCar), a Luminous Blue Variable, is a massive binary star system with a 5.54-year spectroscopic period. We present temporal surface plots of selected He I, H I, Fe II and [N II] stellar line profiles measured with HST/STIS sampled from 1998.0 to 2004.3. Our analysis suggests that the profile variations are due to 1) radial velocity variations of the primary star and 2) ionization effects due to the hot companion combined with its wind cavity.

Blue compact dwarf (BCD) galaxies are low-metallicity objects undergoing violent star formation (Searle & Sargent 1972). We present our ongoing work on integral field spectroscopy (IFS) of the two prototypical BCD galaxies IIZw70 and IZw18 (Papaderos et al. 2002). Two-dimensional spectroscopy allows us to collect simultaneously the spectra of many different regions of an extended object, combining photometry and spectroscopy in the same data set. The great advantage of using IFS for the investigation of galaxies is that it allows us to obtain data on the galaxies' positions, velocity fields and star-forming properties all in one data cube. The observations were taken with the instruments INTEGRAL/WYFFOS at the WHT (ORM, La Palma) and PMAS installed on the 3.5m telescope at the CAHA, covering a spectral range from λ 3600 to 6800 Å. The data are mainly used to study the ionized gas and stellar clusters. Our main goal is to investigate the presence of spatial variations in ionization structure indicators, physical conditions and gaseous metal abundances, in these galaxies (Vílchez & Iglesias-Páramo 1998). We also study the kinematical properties of the ionized gas, as well as systematic variations of ionization structure and physical-chemical parameters as a function of the surface-brightness in Hα emission. Maps of the relevant emission lines are presented.

Using the data from BBSO, YNAO and SOHO/MDI we studied the formation and evolution of a ring-filament which was located in NOAA AR09470 from May 21 to 24, 2001. We found that: (1) the ring-filament's formation was well associated with newly-emerging flux. (2) all the eruptions of the filament happened during the decay of the emerging bipoles.

Results of the SMART-1 mission to Earth's Moon are summarized.

We have developed a robust and efficient algorithm to identify gravitational lensing arcs and interacting galaxies. The algorithm has been applied to the Red Sequence Survey II (RCS II) data, and we demonstrate a few examples here.

We discuss the results of HI survey of the LMC and a catalog of HI clouds.

We present narrow-band images and high resolution long-slit spectra of the compact planetary nebulae M 1-66, He 2-115, K 3-1, K 3-13 and K 3-30, which present evidence of collimated outflows. Our data reveal the internal structure and kinematics of these objects for the first time.

Here we discuss the possibility to use gravitational microlensing in order to probe the geometry around a massive black hole. Taking into account that lensed quasars are emitting X-rays which come from the heart of these objects, we investigated the influence of microlensing on the Fe Kα line shape originated in Schwarzschild and Kerr metrics.

The Canis Major overdensity (CMa) was initially proposed to be the remnant of a tidally disrupting dSph galaxy. Since its nature is still subject of debate, the goal of the present work was to conduct a large-scale RR Lyrae survey in CMa, in order to see if there is an overdensity of these stars. The survey spans a total area of ∼ 34 sq. deg. with observations in V and R filters, made with the 1.0m Jürgen Stock Schmidt telescope at the National Astronomical Observatory of Venezuela. Current results in a subregion, including spectroscopic observations, show that the small number of RR Lyrae stars found can be accounted for by the halo and thick disk components of our Galaxy.

In 1905, Henri Poincaré predicted the existence of gravitational waves and assumed their speed equal to the speed of light. If additionally the gravitational aberration would have the same magnitude as the aberration of light, we would observe several paradoxical phenomena. For instance, the orbit of two bodies would be unstable, since two attractive forces arise that are not in line and hence form a couple. This will be modelled by a nonautonomous system of ordinary differential equations with delay. In fact, any positive value of the gravitational aberration increases the angular momentum of such a system and this may contribute to the expansion of the universe. We found a remarkable coincidence between the Hubble constant and the increasing distance of the Moon from the Earth.

In 2000, Carlip showed that in general relativity gravitational aberration is almost cancelled out by velocity–dependent interactions. We show how the actual value of the gravitational aberration can be obtained by measurement of a single angle at a suitable time t* corresponding to the perihelion of an elliptic orbit. We also derive an a priori error estimate that expresses how accurately t* has to be determined to obtain the gravitational aberration to a prescribed tolerance.

Recent observations suggest that dissipationless mergers of elliptical galaxies build up the population of massive early-type galaxies (Bell et al. 2004; Faber et al. 2006). This type of merger is observed in galaxy clusters (Tran et al. 2005) and predicted by semi-analytic models which find mass assembly times significantly later than star-formation times for the most massive elliptical galaxies (de Lucia & Blaizot 2006). Here, we use a semi-analytic model of minor mergers of dark matter halos to examine the role of dry minor mergers in elliptical galaxy formation.

Black holes surrounded by axisymmetric structures prosper in some of the most interesting sources in the universe. However, a consistent exact description of the gravitational field of these systems is still lacking. In a static case, the task reduces to Laplace equation and the fields of multiple sources follow by mere superposition. In a rotating case, non-linearity of the Einstein equations resists simple grasp, but even then the theory of completely integrable systems seems to verge on satisfactory solutions. It seeks them in terms of θ-functions on special manifolds connected – symptomatically – with the names of Riemann and Hilbert.

We present a population synthesis calculation to derive the total number of planetary nebulae (PNe) in the Galaxy from single stars and binaries. By combining the most up-to-date literature results regarding galactic and stellar formation and evolution, we determined the total number of PNe with radii $<$0.8 pc deriving from single stars and binaries to be 46 000$\pm$15 000. By using common envelope (CE) calculations and observational results of main sequence binaries, we predict that 5 000$\pm$1 600 post-CE PNe with radii $<$0.8 pc exist in the Galaxy today. We compare these predictions with the observationally-based estimate of 7 200$\pm$1 800 PNe in the Galaxy with radii $<$0.8 pc. This suggests that many single stars do not produce PNe and that 69$\pm$28% of PNe we observe derive from CE interactions on the Asymptotic Giant Branch (AGB).