Radio detection of colliding wind binaries

Four massive, early-type stars, three of which are confirmed binaries, have been observed with the Australia Telescope Compact Array at 1.4, 2.4, 4.8, and 8.6 GHz. The earliest star cataloged so far, HD 93129A, was also observed at 17.8 and 24.5 GHz. Here we present an analysis of the spectra as well as the structure of the stellar systems. All four spectra show clear evidence of non-thermal emission, indicative of a binary system with a colliding wind region. We discuss the magnetic field of the emitting region of HD 93129A and make predictions on the radiation at high energies. Archive X-ray observations towards the target sources are also investigated and interpreted in the light of the non-thermal emission detected.Facultad de Ciencias Astronómicas y Geofísica

Discovery of thermal X-ray emission in the supernova remnant G337.8-0.1 (Kes 41)

Aims: We report here on the first detection at X-ray wavelengths of the Supernova Remnant (SNR) G337.8-0.1, carried out with the XMM-Newton Observatory. Methods: Using the X-ray observations, we studied the X-ray morphology of the remnant at different energy ranges, analysed the spectral properties and investigated a possible variable behavior. Results: The SNR shows a diffuse filled-center structure in the X-ray region with an absence of a compact source in its center. We find a high column density of NH > 6.9 × 1022 cm-2, which supports a relatively distant location (d ≥ 7 kpc). The X-ray spectrum exhibits emission lines, indicating that the X-ray emission has a thin thermal plasma origin, and is well represented by a non-equilibrium ionization (NEI) plasma model. The X-ray characteristics and well-known radio parameters show that G337.8-0.1 belongs to the emerging class of mixed-morphology (MM) SNRs.Facultad de Ciencias Astronómicas y Geofísica

Discovery of thermal X-ray emission in the supernova remnant G337.8-0.1 (Kes 41)

Aims: We report here on the first detection at X-ray wavelengths of the Supernova Remnant (SNR) G337.8-0.1, carried out with the XMM-Newton Observatory. Methods: Using the X-ray observations, we studied the X-ray morphology of the remnant at different energy ranges, analysed the spectral properties and investigated a possible variable behavior. Results: The SNR shows a diffuse filled-center structure in the X-ray region with an absence of a compact source in its center. We find a high column density of NH > 6.9 × 1022 cm-2, which supports a relatively distant location (d ≥ 7 kpc). The X-ray spectrum exhibits emission lines, indicating that the X-ray emission has a thin thermal plasma origin, and is well represented by a non-equilibrium ionization (NEI) plasma model. The X-ray characteristics and well-known radio parameters show that G337.8-0.1 belongs to the emerging class of mixed-morphology (MM) SNRs.Facultad de Ciencias Astronómicas y Geofísica

XMM-Newton X-ray observations of the Carina nebula

We use new XMM-Newton observations to perform a detailed X-ray analysis of the Carina nebula region in the 0.3-12 keV energy range. Our source detection yields 80 discrete X-ray sources, from which about 20 per cent seem not to have optical counterparts. To get an idea of the energy spectrum of these sources, we construct an X-ray.colour-colour diagram using the energy bands 0.3-2, 2-4.5 and 4.5-12 keV. We analyse the spectra of the most intense X-ray sources associated with early-type stars, including the luminous blue variable η Carina and WR25. We show that the X-ray emission from these sources is well fitted by multitemperature model spectra. We detect surprisingly intense X-ray emission at energies above 4 keV for some of the observed early-type stars, especially from CPD-59 2629 (Tr16-22) which presents particularly hard X-ray emission. We detect intense soft X-ray emission, below <2 keV, in HDE 303311, which presents an X-ray excess of about 100 times higher than has been observed in other 05V stars. We use these data to construct the L x/Lbol relation for the 0.3-12 and 3.0-12 keV energy ranges, for all the observed O-type stars, plus η Carina and WR25. Most of the bright stars seem to agree with low metallicity spectral models. The L x/Lbol ratio for O-type stars in the 0.3-12 keV range is well fitted by a constant ≈6.04.87.5 × 10 -7, in fair agreement with the canonical expression L x/Lbol ∼ 2 × 10-7 formerly estimated for the 0.3-2.4 keV energy band. In contrast, the Lx/Lbol relation for the 3.0-12 keV range presents a strong deviation from the canonical relation, with a high dispersion of about four orders of magnitude. We also detect intrinsic X-ray time variability in seven sources, over the time-scale of about 50 h covered by the observations. This includes an X-ray flare of about 2-h duration detected in DETWC Tr16 J104429.2-594143, a source probably not physically associated with the Carina nebula. We discuss the different underlying physical mechanisms that can be responsible for the X-ray emission from early-type stars.Facultad de Ciencias Astronómicas y Geofísica

Radio detection of colliding wind binaries

Four massive, early-type stars, three of which are confirmed binaries, have been observed with the Australia Telescope Compact Array at 1.4, 2.4, 4.8, and 8.6 GHz. The earliest star cataloged so far, HD 93129A, was also observed at 17.8 and 24.5 GHz. Here we present an analysis of the spectra as well as the structure of the stellar systems. All four spectra show clear evidence of non-thermal emission, indicative of a binary system with a colliding wind region. We discuss the magnetic field of the emitting region of HD 93129A and make predictions on the radiation at high energies. Archive X-ray observations towards the target sources are also investigated and interpreted in the light of the non-thermal emission detected.Facultad de Ciencias Astronómicas y Geofísica

XMM-Newton X-ray observations of the Carina nebula

We use new XMM-Newton observations to perform a detailed X-ray analysis of the Carina nebula region in the 0.3-12 keV energy range. Our source detection yields 80 discrete X-ray sources, from which about 20 per cent seem not to have optical counterparts. To get an idea of the energy spectrum of these sources, we construct an X-ray.colour-colour diagram using the energy bands 0.3-2, 2-4.5 and 4.5-12 keV. We analyse the spectra of the most intense X-ray sources associated with early-type stars, including the luminous blue variable η Carina and WR25. We show that the X-ray emission from these sources is well fitted by multitemperature model spectra. We detect surprisingly intense X-ray emission at energies above 4 keV for some of the observed early-type stars, especially from CPD-59 2629 (Tr16-22) which presents particularly hard X-ray emission. We detect intense soft X-ray emission, below <2 keV, in HDE 303311, which presents an X-ray excess of about 100 times higher than has been observed in other 05V stars. We use these data to construct the L x/Lbol relation for the 0.3-12 and 3.0-12 keV energy ranges, for all the observed O-type stars, plus η Carina and WR25. Most of the bright stars seem to agree with low metallicity spectral models. The L x/Lbol ratio for O-type stars in the 0.3-12 keV range is well fitted by a constant ≈6.04.87.5 × 10 -7, in fair agreement with the canonical expression L x/Lbol ∼ 2 × 10-7 formerly estimated for the 0.3-2.4 keV energy band. In contrast, the Lx/Lbol relation for the 3.0-12 keV range presents a strong deviation from the canonical relation, with a high dispersion of about four orders of magnitude. We also detect intrinsic X-ray time variability in seven sources, over the time-scale of about 50 h covered by the observations. This includes an X-ray flare of about 2-h duration detected in DETWC Tr16 J104429.2-594143, a source probably not physically associated with the Carina nebula. We discuss the different underlying physical mechanisms that can be responsible for the X-ray emission from early-type stars.Facultad de Ciencias Astronómicas y Geofísica

Discovery of thermal X-ray emission in the supernova remnant G337.8-0.1 (Kes 41)

Aims: We report here on the first detection at X-ray wavelengths of the Supernova Remnant (SNR) G337.8-0.1, carried out with the XMM-Newton Observatory. Methods: Using the X-ray observations, we studied the X-ray morphology of the remnant at different energy ranges, analysed the spectral properties and investigated a possible variable behavior. Results: The SNR shows a diffuse filled-center structure in the X-ray region with an absence of a compact source in its center. We find a high column density of NH > 6.9 × 1022 cm-2, which supports a relatively distant location (d ≥ 7 kpc). The X-ray spectrum exhibits emission lines, indicating that the X-ray emission has a thin thermal plasma origin, and is well represented by a non-equilibrium ionization (NEI) plasma model. The X-ray characteristics and well-known radio parameters show that G337.8-0.1 belongs to the emerging class of mixed-morphology (MM) SNRs.Facultad de Ciencias Astronómicas y Geofísica

G287.84-0.82: an infrared star cluster in the Carina nebula

We have studied the properties of an infrared cluster embedded in the gas and dust of the southern part of the Carina nebula (NGC 3372), where the probable existence of current star formation has already been predicted. We used mid-infrared (A and C bands) and near-infrared (JHKs) images from the Midcourse Space Experiment and the Two-Micron All-Sky Survey, respectively, combined with an optical Ha narrow-band filter image obtained at the Cerro Tololo Inter-American Observatory. The infrared star cluster has at least 17 members, and its parameters, radius and stellar density are in very good agreement with high- to intermediate-mass star formation scenarios. The detected infrared sources have roughly the same intrinsic infrared excess determined from their position in colour-colour and colour-magnitude diagrams, suggesting that these objects could be related to pre-main-sequence stars of high to intermediate mass. Furthermore, we present a low-dispersion spectrum of the LS 1883 (O9.5V) star located near the centre of the infrared cluster. The position of this object in the colour-colour and colour-magnitude infrared diagrams lies close to the reddening vector of a zero-age main-sequence O9V spectral-type star, and it seems to be the first star of this cluster to emerge. All these facts are consistent with the current star-forming scenarios associated with highly embedded star clusters.Facultad de Ciencias Astronómicas y Geofísica

Elemental abundance study of the CP star HD 206653

An analysis of the abundances of the Silicon star HD 206653 is presented using an ATLAS9 model atmosphere and observational material taken with a REOSC echelle spectrograph attached to the Jorge Sahade 2.15 m telescope at CASLEO. The light elements are solar or deficient except silicon which is overabundant by a factor of 5. The iron peak elements are all overabundant by factors between 10 and 50. Sr and Y are around 1000 times the solar values. Among the Rare Earths only Ce and Eu are identified; both are overabundant by large factors.Facultad de Ciencias Astronómicas y Geofísica

Elemental abundance study of the CP star HD 206653

An analysis of the abundances of the Silicon star HD 206653 is presented using an ATLAS9 model atmosphere and observational material taken with a REOSC echelle spectrograph attached to the Jorge Sahade 2.15 m telescope at CASLEO. The light elements are solar or deficient except silicon which is overabundant by a factor of 5. The iron peak elements are all overabundant by factors between 10 and 50. Sr and Y are around 1000 times the solar values. Among the Rare Earths only Ce and Eu are identified; both are overabundant by large factors.Facultad de Ciencias Astronómicas y Geofísica