Publikacje w roku 2006
Dust at Low Metallicity: Spitzer Observations of AGB Stars in NGC 6822
Van Dyk, S. D., Kemper, F., Speck, A., Szczerba, R., Meixner, M., Peeters, E., and Ueta, T.
2006 , 2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #168.13; Bulletin of the American Astronomical Society, Vol. 38, p.1140
Dust condensation may depend heavily on the metallicity, although the effect is poorly known. The total condensed dust mass from stars at low metallicity could be lower, there could be more simple oxides and fewer silicates, and the degree of silicate crystallinity could be lower. We have obtained mid-infrared spectra with the Spitzer Space Telescope of a sample of 20 Cand O-rich asymptotic giant branch (AGB) stars in the Local Group dwarf galaxy NGC 6822. To our knowledge this is the first time such evolved stars have been spectroscopically observed in this galaxy. We compare our results to those for AGB stars in the Galaxy and in the Magellanic Clouds. We intend to contribute to an improved understanding of dust formation in general and to provide the ability to use grain properties and dust composition as a tool to trace physical conditions in nearby galaxies. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.
Eruptions of the V838 Mon type: stellar merger versus nuclear outburst models
Tylenda, R. and Soker, N.
2006 , Astronomy and Astrophysics, Volume 451, Issue 1, May III 2006, pp.223-236
We discuss various models and scenarios proposed to explain the nature of the V838 Mon type eruptions. In this class of eruptive objects we include: M 31 RV (erupted in 1988), V4332 Sgr (erupted in 1994) and V838 Mon (erupted in 2002). We concentrate on three models: (i) thermonuclear runaway on an accreting white dwarf (nova-like event); (ii) He-shell flash in a post asymptotic giant branch star (born-again AGB); and (iii) merger of stars. We show that models (i) and (ii) cannot account for the majority of the observed properties of the objects. Most significantly, in both nuclear burning type models the object is expected to heat up before declining and fade as a very hot compact star. In the observed eruptions the objects declined as very cool giants or supergiants. We show that the stellar merger model can account for all the observed properties and conclude that presently this is the most promising model to explain the eruptions of the V838 Mon type.
A warped m = 2 water maser disc in V778 Cyg?
Babkovskaia, N., Poutanen, J., Richards, A. M. S., and Szczerba, R.
2006 , Monthly Notices of the Royal Astronomical Society, Volume 370, Issue 4, pp. 1921-1927.
The silicate carbon star V778 Cyg is a source of 22-GHz water maser emission which was recently resolved by MERLIN. Observations revealed an elongated -like structure along which the velocities of the maser features show a linear dependence on the impact parameter. This is consistent with a doubly warped m = 2 disc observed edge-on. Water masers and silicate dust emission (detected by the Infrared Astronomical Satellite and Infrared Space Observatory) have a common origin in O-rich material and are likely to be co-located in the disc. We propose a detailed self-consistent model of a masing gas-dust disc around a companion to the carbon star in a binary system, which allows us to estimate the companion mass of 1.7 +/- 0.1Msolar, the disc radius of 40 +/- 3 au and the distance between companions of ~80 au. Using a dust-gas coupling model for water masing, we calculate the maser power self-consistently, accounting for both the gas and the dust energy balances. Comparing the simulation results with the observational data, we deduce the main physical parameters of the masing disc, such as the gas and dust temperatures and their densities. We also present an analysis of the stability of the disc.
Carbon and oxygen stars evolution in post-AGB phase
Siódmiak, N., Szczerba, R., Meixner, M., and Stasińska, G.
2006 , Planetary Nebulae in our Galaxy and Beyond, Proceedings of the International Astronomical Union, Symposium #234. Edited by Michael J. Barlow and Roberto H. Méndez. Cambridge: Cambridge University Press, 2006., pp.511-512
Despite many studies, the post-AGB phase is still not well understood. To make progress in this field, we searched for information about proto-planetary nebulae and built a catalogue of post-AGB objects. Based on collected data we were able to trace the evolution of stars in their late stages making a distinction between carbon and oxygen-rich objects. We focused our attention on spectral features seen in ISO data and clues for AGB nucleosynthesis. Together with the newest HST images of post-AGB objects we can study correlations between morphological types and chemical and physical properties of stars to improve our understanding of stellar evolution.
Detached shells as tracers of asymptotic giant branch-interstellar medium bow shocks
Wareing, C. J., Zijlstra, A. A., Speck, A. K., O'Brien, T. J., Ueta, T., Elitzur, M., Gehrz, R. D., Herwig, F., Izumiura, H., Matsuura, M., Meixner, M., Stencel, R. E., and Szczerba, R.
2006 , Monthly Notices of the Royal Astronomical Society: Letters, Volume 372, Issue 1, pp. L63-L67.
New Spitzer imaging observations have revealed the structure around the Mira variable star R Hya to be a one-sided parabolic arc 100 arcsec to the west, stretching from north to south. We successfully model R Hya and its surroundings in terms of an interaction of the stellar wind from an asymptotic giant branch (AGB) star with the interstellar medium (ISM) the star moves through. Our three-dimensional hydrodynamic simulation reproduces the structure as a bow shock into the oncoming ISM. We propose this as another explanation of detached shells around such stars, which should be considered alongside current theories of internal origin. The simulation predicts the existence of a tail of ram-pressure-stripped AGB material stretching downstream. Indications for such a tail behind R Hya are seen in IRAS maps.
Detection of a Far-Infrared Bow Shock Nebula around R Hya: The First MIRIAD Results
Ueta, T., Speck, A. K., Stencel, R. E., Herwig, F., Gehrz, R. D., Szczerba, R., Izumiura, H., Zijlstra, A. A., Latter, W. B., Matsuura, M., Meixner, M., Steffen, M., and Elitzur, M.
2006 , The Astrophysical Journal, Volume 648, Issue 1, pp. L39-L42.
We present the first results of the MIRIAD (MIPS InfraRed Imaging of AGB Dust shells) project using the Spitzer Space Telescope. The primary aim of the project is to probe the material distribution in the extended circumstellar envelopes (CSEs) of evolved stars and recover the fossil record of their mass-loss history. Hence, we must map the whole of the CSEs plus the surrounding sky for background subtraction while avoiding the central star that is brighter than the detector saturation limit. With our unique mapping strategy, we have achieved better than 1 MJy sr-1 sensitivity in 3 hr of integration and successfully detected a faint (<5 MJy sr-1), extended (~400") far-infrared nebula around the asymptotic giant branch (AGB) star R Hya. Based on the parabolic structure of the nebula, the direction of the space motion of the star with respect to the nebula shape, and the presence of extended Hα emission cospatial to the nebula, we suggest that the detected far-IR nebula is due to a bow shock at the interface of the interstellar medium and the AGB wind of this moving star. This is the first detection of the stellar-wind bow shock interaction for an AGB star and exemplifies the potential of Spitzer as a tool to examine the detailed structure of extended far-IR nebulae around bright central sources.
New small planetary nebulae discovered in the Galactic center direction
Górny, S. K.
2006 , Planetary Nebulae in our Galaxy and Beyond, Proceedings of the International Astronomical Union, Symposium #234. Edited by Michael J. Barlow and Roberto H. M&eacute;ndez. Cambridge: Cambridge University Press, 2006., pp.409-410
During an ongoing search #for small planetary nebulae in the southern hemisphere 24 candidates have been found and spectroscopically observed in a region of 45 square degrees.
Orbital Configurations and Dynamical Stability of Multiplanet Systems around Sun-like Stars HD 202206, 14 Herculis, HD 37124, and HD 108874
Goździewski, K., Konacki, M., and Maciejewski, A. J.
2006 , The Astrophysical Journal, Volume 645, Issue 1, pp. 688-703.
We perform a dynamical analysis of the recently published radial velocity (RV) measurements of a few solar-type stars that host multiple Jupiter-like planets. In particular, we reanalyze the data for HD 202206, 14 Her, HD 37124, and HD 108874. We derive dynamically stable configurations that reproduce the observed RV signals, using GAMP (the genetic algorithm with MEGNO penalty). GAMP relies on N-body dynamics and makes use of genetic algorithms merged with a stability criterion. For this purpose, we use the maximal Lyapunov exponent computed with the dynamical fast indicator MEGNO. Through a dynamical analysis of the phase space in a neighborhood of the obtained best-fit solutions, we derive meaningful limits on the parameters of the planets. We demonstrate that GAMP is especially well suited to the analysis of the RV data that only partially cover the longest orbital period and/or are related to multiplanet configurations involved in low-order mean motion resonances (MMRs). Our analysis reveals a presence of a second Jupiter-like planet in the 14 Her system (14 Her c) that is involved in a 3:1 or 6:1 MMR with the known companion 14 Her b. We also show that the dynamics of the HD 202206 system may be qualitatively different when coplanar and mutually inclined orbits of the companions are considered. We demonstrate that the two outer planets in the HD 37124 system may reside in a close neighborhood of the 5:2 MMR. Our results confirm that the HD 108874 system may be very close to a, or locked in an exact, 4:1 MMR.
Oxygen-rich disk in the V778 Cygni system resolved
Szczerba, R., Szymczak, M., Babkovskaia, N., Poutanen, J., Richards, A. M. S., and Groenewegen, M. A. T.
2006 , Astronomy and Astrophysics, Volume 452, Issue 2, June III 2006, pp.561-565
Aims.Various scenarios have been proposed to explain the presence of silicate features associated with carbon stars, such as V778 Cyg. We have attempted to constrain these theories by means of mapping water maser emission from V778 Cyg.

Methods. .The 22 GHz water maser emission from this star has been mapped using MERLIN with an astrometric accuracy of 25 mas.

Results. .The spatially- and kinematically-resolved maser complex is displaced by ~190 mas from the position of the C-star as measured 10 years earlier using Tycho. Our simulations and analysis of available data show that this position difference is unlikely to be due to proper motion if V778 Cyg is at the assumed distance of 1.4 kpc. The maser components seem to form a distorted S-shaped structure extended over ~18 mas with a clear velocity gradient. We propose a model which explains the observed water maser structure as an O-rich warped disk around a companion of the C-star in V 778 Cyg binary system, which is seen almost edge-on.

Conclusions. .Analysis of observational data, especially those obtained with MERLIN, suggests that V778 Cyg (and, by implication, other silicate carbon stars) are binary systems composed of a C-rich star and a companion which stores circumstellar O-rich material.
PHASES: A Search for Planets in Binary Systems
Lane, B., Muterpspaugh, M., Konacki, M., Kulkarni, S., Shao, M., Colavita, M., and Burke, B.
2006 , 2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #241.04; Bulletin of the American Astronomical Society, Vol. 38, p.1228
For the past three years we have used the Palomar Testbed Interferometer to undertake an astrometric search for planets in binary stellar systems. By using phase referencing and long-baseline near-IR interferometry we are able to obtain an astrometric precision of approximately 20 micro-arcseconds between pairs of stars with separations in the range 0.1-1 arcsecond. We have followed 40 systems intensively and to date have over 800 astrometric measurements. We will present results from the first comprehensive analysis of this data set, including strong limits on the occurrence of planets in our target systems. The PHASES program serves as an excellent precursor to the type of program we expect to undertake with the Space Interferometry Mission PlanetQuest.
PHASES Differential Astrometry and Iodine Cell Radial Velocities of the κ Pegasi Triple Star System
Muterspaugh, M. W., Lane, B. F., Konacki, M., Wiktorowicz, S., Burke, B. F., Colavita, M. M., Kulkarni, S. R., and Shao, M.
2006 , The Astrophysical Journal, Volume 636, Issue 2, pp. 1020-1032.
κ Pegasi is a well-known, nearby triple star system. It consists of a ``wide'' pair with semimajor axis=235 mas, one component of which is a single-line spectroscopic binary (semimajor axis= 2.5 mas). Using high-precision differential astrometry and radial velocity observations, the masses for all three components are determined and the relative inclination between the wide and narrow pairs' orbits is found to be 43.8d+/-3.0d, just over the threshold for the three-body Kozai resonance. The system distance is determined to be 34.60+/-0.21 pc and is consistent with trigonometric parallax measurements.
PHASES differential astrometry and the mutual inclination of the V819 Herculis triple star system
Muterspaugh, M. W., Lane, B. F., Konacki, M., Burke, B. F., Colavita, M. M., Kulkarni, S. R., and Shao, M.
2006 , Astronomy and Astrophysics, Volume 446, Issue 2, February I 2006, pp.723-732
V819 Herculis is a well-studied triple star system consisting of a
"wide" pair with 5.5 year period, one component of which is a 2.2-day period eclipsing single-line spectroscopic binary. Differential astrometry measurements from the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES) are presented and used to determine a relative inclination between the short- and long-period orbits of 23.6 ± 4.9 degrees. This represents only the sixth unambiguous determination of the mutual inclination of orbits in a hierarchical triple system. This result is combined with those for the other five systems for analysis of the observed distribution of mutual inclinations in nearby triple systems. It is found that this distribution is different than that which one would expect from random orientations with statistical significance at the 94% level; implications for studying the spatial distribution of angular momentum in star forming regions is discussed.
Planetary nebulae with emission-line central stars
Gesicki, K., Zijlstra, A. A., Acker, A., Górny, S. K., Gozdziewski, K., and Walsh, J. R.
2006 , Astronomy and Astrophysics, Volume 451, Issue 3, June I 2006, pp.925-935
The kinematic structure of a sample of planetary nebulae, consisting of 23 [WR] central stars, 21 weak emission line stars (wels), and 57 non-emission line central stars, is studied. The [WR] stars are shown to be surrounded by turbulent nebulae, a characteristic shared by some wels but almost completely absent from the non-emission line stars. The fraction of objects showing turbulence for non-emission-line stars, wels, and [WR] stars is 7%, 24%, and 91%, respectively. The [WR] stars show a distinct IRAS 12-micron excess, indicative of small dust grains, which is not found for wels. The [WR]-star nebulae are on average more centrally condensed than those of other stars. On the age-temperature diagram, the wels are located on tracks of both high and low stellar mass, while [WR] stars trace a narrow range of intermediate masses. Emission-line stars are not found on the cooling track. One group of wels may form a sequence wels-[WO] stars with increasing temperature. For the other groups, both the wels and the [WR] stars appear to represent several, independent evolutionary tracks. We find a discontinuity in the [WR] stellar temperature distribution and suggest different evolutionary sequences above and below the temperature gap. One group of cool [WR] stars has no counterpart among any other group of PNe and may represent binary evolution. A prime factor distinguishing wels and [WR] stars appears to be stellar luminosity. We find no evidence for an increase in the nebular expansion velocity with time.
Post-AGB stars as testbeds of nucleosynthesis in AGB stars
Stasińska, G., Szczerba, R., Schmidt, M., and Siódmiak, N.
2006 , Astronomy and Astrophysics, Volume 450, Issue 2, May I 2006, pp.701-714
We construct a data base of 125 post-AGB objects (including R CrB and extreme helium stars) with published photospheric parameters (effective temperature and gravity) and chemical composition. We estimate the masses of the post-AGB stars by comparing their position in the (log T{eff}, log g) plane with theoretical evolutionary tracks of different masses. We construct various diagrams, with the aim of finding clues to AGB nucleosynthesis. This is the first time that a large sample of post-AGB stars has been used in a systematic way for such a purpose and we argue that, in several respects, post-AGB stars should be more powerful than planetary nebulae to test AGB nucleosynthesis. Our main findings are that: the vast majority of objects which do not show evidence of N production from primary C have a low stellar mass (Mstar < 0.56 M); there is no evidence that objects which did not experience 3rd dredge-up have a different stellar mass distribution than objects that did; there is clear evidence that 3rd dredge-up is more efficient at low metallicity. The sample of known post-AGB stars is likely to increase significantly in the near future thanks to the ASTRO-F and follow-up observations, making these objects even more promising as testbeds for AGB nucleosynthesis.
Scientific results from high-precision astrometry at the Palomar Testbed Interferometer
Muterspaugh, M. W., Lane, B. F., Konacki, M., Burke, B. F., Colavita, M. M., Kulkarni, S. R., and Shao, M.
2006 , Advances in Stellar Interferometry. Edited by Monnier, John D.; Sch&ouml;ller, Markus; Danchi, William C.. Proceedings of the SPIE, Volume 6268, pp. 62680F (2006).
A new observing mode for the Palomar Testbed Interferometer was developed in 2002-2003 which enables differential astrometry at the level of 20 micro-arcseconds (μas) for binary systems with separations of several hundred milli-arcseconds (mas). This phase-referenced mode is the basis of the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES), a search for giant planets orbiting either the primary or secondary star in fifty binary systems. We present the first science results from the PHASES search. The properties of the stars comprising binary systems are determined to high precision. The mutual inclinations of several hierarchical triple star systems have been determined. We will present upper limits constraining the the existence of giant planets in a few of the target systems.
Short GRB progenitors: population synthesis predictions vs. observations
Bulik, T., Belczyński, K., and Rudak, B.
2006 , GAMMA-RAY BURSTS IN THE SWIFT ERA: Sixteenth Maryland Astrophysics Conference. AIP Conference Proceedings, Volume 836, pp. 68-71 (2006).
One of the leading models for the progenitors of of short GRBs are compact object mergers. The properties of coalescing compact object binaries have been obtained with the population synthesis method. The results show the differences between the NSNS and BHNS mergers. I review the status of these two models of short GRBs in the light of recently observed short bursts and their host galaxies.
The Shadow of a Pulsar and the Inward Radio Emission in Pulsar Magnetosphere
Dyks, J., Frackowiak, M., Słowikowska, A., Rudak, B., and Zhang, B.
2006 , Chinese Journal of Astronomy and Astrophysics, Supplement, Volume 6, Issue S2, Proceedings of the 2005 Lake Hanas International Pulsar Symposium. Editors: N. Wang, R. N. Manchester, B. J. Rickett and A. Esamdin., p.85-89
We discuss observational facts that can be interpreted in terms of inward emission in pulsar magnetosphere. These include the main-pulse/interpulse anticorrelation in B1822-09 and the locations of emission and absorption features in the pulse profile of B0950+08. Weaknesses of geometrical models employing the inward emission are carefully discussed.
The Unusual Spitzer Spectrum of the Carbon Star IRAS 04496-6958: A Different Condensation Sequence in the LMC?
Speck, A. K., Cami, J., Markwick-Kemper, C., Leisenring, J., Szczerba, R., Dijkstra, C., Van Dyk, S., and Meixner, M.
2006 , The Astrophysical Journal, Volume 650, Issue 2, pp. 892-900.
We present a new Spitzer Infrared Spectrograph (IRS) spectrum of the carbon star IRAS 04496-6958 in the Large Magellanic Cloud, which exhibits a fairly broad absorption feature at ~11 μm. This feature is consistent with SiC absorption, as seen in a few Galactic sources. Furthermore, the C2H2 (and other molecular) absorption bands are the deepest ever observed, indicative of a very high column density. While the Galactic sources with SiC absorption have cool colors (continuum temperature ~300 K), IRAS 04496-6958 is much bluer, with a continuum temperature of ~600 K. Based on the Galactic sample, SiC dust at this temperature should still display an emission feature at ~11 μm. If SiC is the cause of the absorption feature, it suggests a subtly different evolutionary path and a change to a different condensation sequence than assumed for Galactic carbon stars. An alternative explanation for this feature is molecular line absorption; however, currently available line lists are not sufficient to properly assess this hypothesis.
Trojan Pairs in the HD 128311 and HD 82943 Planetary Systems?
Goździewski, K. and Konacki, M.
2006 , The Astrophysical Journal, Volume 647, Issue 1, pp. 573-586.
Two nearby stars, HD 128311 and HD 82943, are believed to host pairs of Jupiter-like planets involved in a strong first-order 2:1 mean motion resonance (MMR). In this work, we reanalyze available radial velocity (RV) measurements and demonstrate that it is also possible to explain the observed RV variations of the parent stars as being induced by a pair of Trojan planets (i.e., in a 1:1 MMR). We show that these Trojan configurations reside in extended zones of stability in which such systems can easily survive in spite of the large masses of the planets, large eccentricities, and nonzero mutual inclinations of their orbits. We also show that HD 82943 could harbor a previously unknown third planet of ~0.5MJ in ~2 AU orbit.
Using Planetary nebulae to determine the abundance gradient in the Galaxy
Peña, M., Stasińska, G., and Gorny, S. G.
2006 , XI IAU Regional Latin American Meeting of Astronomy (Eds. L. Infante &amp; M. Rubio) Revista Mexicana de Astronom&iacute;a y Astrof&iacute;sica (Serie de Conferencias) Vol. 26, pp. 24-25 (2006)
We discuss some problems on the determination of galactic abundance gradients in the Milky Way using planetary nebulae. We reexamine the O/H gradient based on a large homogeneous sample of objects and propose a new method to determine the distances to the PNe.
Violent stellar merger model for transient events
Soker, N. and Tylenda, R.
2006 , Monthly Notices of the Royal Astronomical Society, Volume 373, Issue 2, pp. 733-738.
We derive the constraints on the mass ratio for a binary system to merge in a violent process. We find that the secondary-to-primary stellar mass ratio should be 0.003 <~ (M2/M1) <~ 0.15. A more massive secondary star will keep the primary stellar envelope in synchronized rotation with the orbital motion until merger occurs. This implies a very small relative velocity between the secondary star and the primary stellar envelope at the moment of merger, and therefore very weak shock waves, and low-flash luminosity. A too low-mass secondary will release small amount of energy, and will expel small amount of mass, which is unable to form an inflated envelope. It can, however, produce a quite luminous but short flash when colliding with a low-mass main-sequence star.
Violent and luminous mergers, which we term mergebursts, can be observed as V838 Monocerotis-type events, where a star undergoes a fast brightening lasting days to months, with a peak luminosity of up to ~106Lsolar followed by a slow decline at very low effective temperatures.
VIRGO sensitivity to binary coalescences and the Population III black hole binaries
Kulczycki, K., Bulik, T., Belczyński, K., and Rudak, B.
2006 , Astronomy and Astrophysics, Volume 459, Issue 3, December I 2006, pp.1001-1006
Aims.We analyze the properties of VIRGO detector with the aim of studying its ability to search for coalescing black hole binaries. We focus on the remnants of the Population III stars, which currently should be massive black holes (˜ 100{-}1000 M_⊙), some of them bound in binary systems. The coalescence of such binaries due to emission of gravitational waves may be currently observable.

Methods. .We use a binary population synthesis to model the evolution of Population III binaries.

Results. . We calculate the signal to noise ratios of gravitational waves emitted by the system in each of the coalescence phase: inspiral, merger and ringdown, and provide simple formulae for the signal to noise ratio as a function of masses of the binaries. We estimate the detection rates for the VIRGO interferometer and also compare them with the estimates for the current LIGO. We show that these expected rates are similar to, or larger than the expected rates from coalescences of Population I and II compact object binaries.
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