G. Skalkowski

Université de Montréal, Montréal, Quebec, Canada

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Publications (6)16.77 Total impact

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    ABSTRACT: NGC 3603 is the most massive and luminous visible starburst region in the Galaxy. We present the first Chandra ACIS-I X-ray image and spectra of this dense, exotic object, accompanied by a deep centimeter-wavelength Australia Telescope Compact Array radio image at similar 1'' spatial resolution and Hubble Space Telescope/ground-based optical data. At the S/N > 3 level, Chandra detects several hundred X-ray point sources (compared to the three distinct sources seen by ROSAT). At least 40 of these sources are definitely associated with optically identified cluster O- and W-R-type members, but most are not. A diffuse X-ray component is also seen out to ~2' (4 pc) from the center, probably arising mainly from the large number of merging/colliding hot stellar winds and/or numerous faint cluster sources. The point-source X-ray fluxes generally increase with increasing bolometric brightnesses of the member O/W-R stars, but with very large scatter. Some exceptionally bright stellar X-ray sources may be colliding wind binaries. The radio image shows (1) two resolved sources, one definitely nonthermal, in the cluster core near where the X-ray/optically brightest stars with the strongest stellar winds are located, (2) emission from all three known proplyd-like objects (with thermal and nonthermal components), and (3) many thermal sources in the peripheral regions of triggered star formation. Overall, NGC 3603 appears to be a somewhat younger and hotter scaled-down version of typical starbursts found in other galaxies.
    The Astrophysical Journal 12/2008; 573(1):191. · 6.28 Impact Factor
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    ABSTRACT: High-quality, blue-violet spectroscopic data are collected for 24 stars that have been classified as type O3 and that display the hallmark N IV and N V lines. A new member of the class is presented; it is the second known in the Cyg OB2 association, and only the second in the northern hemisphere. New digital data are also presented for several of the other stars. Although the data are inhomogeneous, the uniform plots by subcategory reveal some interesting new relationships. Several issues concerning the classification of the hottest O-type spectra are discussed, and new digital data are presented for the five original O3 dwarfs in the Carina Nebula, in which the N IV, N V features are very weak or absent. New spectral types O2 and O3.5 are introduced here as steps toward resolving these issues. The relationship between the derived absolute visual magnitudes and the spectroscopic luminosity classes of the O2–O3 stars shows more scatter than at later O types, at least partly because some overluminous dwarfs are unresolved multiple systems, and some close binary systems of relatively low luminosity and mass emulate O3 supergiant spectra. However, it also appears that the behavior of He II λ4686, the primary luminosity criterion at later O types, responds to other phenomena in addition to luminosity at spectral types O2–O3. There is evidence that these spectral types may correspond to an immediate pre-WN phase, with a correspondingly large range of luminosities and masses. A complete census of spectra classified into the original O3 subcategories considered here (not including intermediate O3/WN types or O3 dwarfs without N IV, N V features) totals 45 stars; 34 of them belong to the Large Magellanic Cloud and 20 of the latter to 30 Doradus.
    The Astronomical Journal 12/2007; · 4.97 Impact Factor
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    ABSTRACT: We present the results of an optical spectroscopic study of the massive Wolf–Rayet (WR) binary HD 192641 = WR 137. These 1986–2000 data cover the dust-formation maximum in 1997. Combining all available measurements of radial velocities, we derive, for the first time, a spectroscopic orbit with period 4766 ± 66 d (13.05 ± 0.18 yr). The resulting masses, adopting i= 67 °, are MO= 20 ± 2 M⊙ for the O component and MWR= 4.4 ± 1.5 M⊙ for the WR component. These appear, respectively, approximately normal and on the low side for the given spectral types. Analysis of the intense multisite spectroscopic monitoring in 1999 shows that the C iiiλ5696 and C ivλλ5802/12 lines have the highest intrinsic variability levels. The periodogram analysis yields a small-amplitude modulation in the absorption troughs of the C ivλλ5802/12 and He iλ5876 lines with a period of 0.83 d, which could be related either to pulsations or large-scale rotating structures as seen in the WN4 star EZ Canis Majoris (WR 6). Wavelet analysis of the strong emission lines of C iiiλ5696 and C ivλλ5802/12 enabled us to isolate and follow for several hours small structures (emission subpeaks) associated with density enhancements within the wind of the Wolf–Rayet star. Cross-correlating the variability patterns seen in different lines, we find a weak but significant correlation between the variability in emission lines with different ionization potentials, i.e. in lines formed at different distances from the WR stellar core. Adopting a β wind-velocity law, from the motion of individual subpeaks we find β∼ 5, which is significantly larger than the canonical value β≃ 1 found in O star winds.
    Monthly Notices of the Royal Astronomical Society 05/2005; 360(1):141 - 152. · 5.52 Impact Factor
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    ABSTRACT: We present very preliminary results of a spectroscopic survey of all known 47 WNL stars in the LMC.
    Proceedings of the International Astronomical Union 01/2003;
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    ABSTRACT: The massive star cluster NGC 3603, the ionizing source of a Galactic supergiant HII region, has long been thought of as a nearby analog to more distant starburst galaxies. As such, it is an interesting and useful object of study for stellar and galactic astronomers alike. We have obtained a 50 ksec observation of this region using the CHANDRA X-ray observatory. The high stellar density in the core and the distance to the cluster ( 7 kpc), however, render the stars in the core unresolved even to CHANDRA. In order to properly determine the X-ray luminosities of the stars in the core, and to examine the evidence for diffuse X-ray emission near the core, we have attempted to "reconvolve" the X-ray image by simulating the expected distribution of X-ray photons. As a template, we have used an optical image of the stars in the cluster obtained by the HST Planetary Camera. We find that we can produce the observed CHANDRA image of the core of the cluster using this technique, as well as derive constrained source luminosities for all the member stars in the core. In addition, we show that the observed contribution of diffuse X-ray emission is generally small in the core, though there are some limited regions devoid of strong stellar emission where diffuse X-ray emission may be important. This work was supported by NASA and the Chandra project (award number GO0-1047Z).
    11/2001;
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    ABSTRACT: We present the first Chandra/ACIS-I X-ray images of the supergiant Galactic HII/starforming region NGC 3603. We resolve the emission into (conservatively) ~ 100 stellar objects, and compare our high resolution Chandra X-ray images of the core cluster to high-resolution optical images obtained by HST. The detected sources apparently include most of the massive O stars, some WR stars (which may show evidence of emission produced in wind-wind collisions), and some surprisingly bright emission from relatively late type stars and PMS stars. We present preliminary source identifications from comparison with optical images and present a preliminary Lx}/L{bol relation for the massive X-ray sources.
    10/2000;