References of "Rauw, Grégor"
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See detailA survey for gamma-ray emission from OB associations with INTEGRAL: some preliminary results
Leyder, Jean-Christophe ULg; Rauw, Grégor ULg

in Massive Stars and High-Energy Emission in OB Associations (2005, November 01)

Recent studies indicated that there might be a correlation between OB associations and unidentified gamma-ray sources from the 3EG catalogue. Moreover, when extrapolating the fluxes measured by EGRET at ... [more ▼]

Recent studies indicated that there might be a correlation between OB associations and unidentified gamma-ray sources from the 3EG catalogue. Moreover, when extrapolating the fluxes measured by EGRET at energies higher than 100 MeV with a power-law down to the energy range of ISGRI, the expected count rates should be large enough to be detected with INTEGRAL. As most of these OB associations are located within the Galactic plane, they are being observed by INTEGRAL as part of the Core Program (CP) during both the Galactic Plane Scans (GPS) and the Galactic Center Deep Exposure (GCDE). Combining public and CP data, we have performed a survey for gamma-ray emission from OB associations and the first results are presented in this paper. [less ▲]

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See detailOn the multiplicity of the non-thermal radio emitters 9 Sgr and HD 168112
Rauw, Grégor ULg; Sana, H.; Gosset, Eric ULg et al

in Massive Stars and High-Energy Emission in OB Associations (2005, November)

We discuss the first results of our ongoing optical spectroscopic monitoring campaign of the two O-type stars 9 Sgr and HD 168112. Both objects display a non-thermal radio emission and were considered as ... [more ▼]

We discuss the first results of our ongoing optical spectroscopic monitoring campaign of the two O-type stars 9 Sgr and HD 168112. Both objects display a non-thermal radio emission and were considered as single stars. Based on a large set of high-resolution spectra, we find that 9 Sgr is clearly an eccentric SB2 binary with an orbital period of several years. On the other hand, no evidence for radial velocity variations attributable to binary motion is found in our spectra of HD 168112. [less ▲]

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See detailXMM-Newton observations of the Cyg OB2 association
Rauw, Grégor ULg; De Becker, Michaël ULg; Linder, Natacha ULg

in Massive Stars and High-Energy Emission in OB Associations (2005, November)

We present the first results of an observing campaign of the Cyg OB2 association with the XMM-Newton observatory. The brightest OB-type stars exhibit rather hard spectra suggesting that at least part of ... [more ▼]

We present the first results of an observing campaign of the Cyg OB2 association with the XMM-Newton observatory. The brightest OB-type stars exhibit rather hard spectra suggesting that at least part of their X-ray emission arises in a wind-wind interaction. The EPIC images reveal a large number of fainter X-ray sources most of which are probably low-mass pre-main sequence stars belonging to Cyg OB2. [less ▲]

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See detailEvidence for phase-locked X-ray variations from the colliding-wind massive binary Cyg OB2 #8A
De Becker, Michaël ULg; Rauw, Grégor ULg

in Rauw, G.; Nazé, Y.; Blomme, R. (Eds.) et al Massive Stars and High-Energy Emission in OB Associations (2005, November)

We report on preliminary results of a multi-observatory investigation of the X-ray emission from the massive colliding wind binary Cyg OB2 #8A (O6If + O5.5III(f)). On the basis of our new XMM-Newton-EPIC ... [more ▼]

We report on preliminary results of a multi-observatory investigation of the X-ray emission from the massive colliding wind binary Cyg OB2 #8A (O6If + O5.5III(f)). On the basis of our new XMM-Newton-EPIC observations, along with archive ASCA-SIS and ROSAT-PSPC data, we show strong evidence for a significant phase-locked variability of the X-ray emission from Cyg OB2 #8A with the period of 21.9 days determined by De Becker et al. (2004). These results lend further support to the colliding wind scenario that was already suggested by optical data (De Becker & Rauw 2005). We briefly discuss the behaviour of the X-ray emission from this binary system as a function of phase in the context of the colliding wind scenario. [less ▲]

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See detailMassive Stars and High-Energy Emission in OB Associations
Rauw, Grégor ULg; Nazé, Yaël ULg; Blomme, Ronny et al

Book (2005)

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See detailThe massive binary CPD-41 degrees 7742 - II. Optical light curve and X-ray observations
Sana, H.; Antokhina, E.; Royer, P. et al

in Astronomy and Astrophysics (2005), 441(1), 213-229

In the first paper of this series, we presented a detailed high-resolution spectroscopic study of CPD - 41 degrees 7742, deriving for the first time an orbital solution for both components of the system ... [more ▼]

In the first paper of this series, we presented a detailed high-resolution spectroscopic study of CPD - 41 degrees 7742, deriving for the first time an orbital solution for both components of the system. In this second paper, we focus on the analysis of the optical light curve and on recent XMM-Newton X-ray observations. In the optical, the system presents two eclipses, yielding an inclination i similar to 77 degrees. Combining the constraints from the photometry with the results of our previous work, we derive the absolute parameters of the system. We confirm that the two components of CPD- 41 degrees 7742 are main sequence stars (O9 V+ B1 - 1.5 V) with masses (M-1 similar to 18 M-. and M-2 similar to 10 M-.) and respective radii (R-1 similar to 7.5 R-. and R-2 similar to 5.4 R-.) close to the typical values expected for such stars. We also report an unprecedented set of X-ray observations that almost uniformly cover the 2.44-day orbital cycle. The X-ray emission from CPD-41 degrees 7742 is well described by a two-temperature thermal plasma model with energies close to 0.6 and 1.0 keV, thus slightly harder than typical early-type emission. The X-ray light curve shows clear signs of variability. The emission level is higher when the primary is in front of the secondary. During the high emission state, the system shows a drop of its X-ray emission that almost exactly matches the optical eclipse. We interpret the main features of the X-ray light curve as the signature of a wind-photosphere interaction, in which the overwhelming primary O9 star wind crashes into the secondary surface. Alternatively the light curve could result from a wind-wind interaction zone located near the secondary star surface. As a support to our interpretation, we provide a phenomenological geometric model that qualitatively reproduces the observed modulations of the X-ray emission. [less ▲]

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See detailAn XMM-Newton observation of the multiple system HD 167971 (O5-8V+O5-8V+(O81)) and the young open cluster NGC6604
De Becker, Michaël ULg; Rauw, Grégor ULg; Blomme, Ronny et al

in Astronomy and Astrophysics (2005), 437(3), 1029-1046

We discuss the results of two XMM-Newton observations of the open cluster NGC 6604 obtained in April and September 2002. We concentrate mainly on the multiple system HD 167971 (O5- 8V + O5- 8V + (O8I ... [more ▼]

We discuss the results of two XMM-Newton observations of the open cluster NGC 6604 obtained in April and September 2002. We concentrate mainly on the multiple system HD 167971 (O5- 8V + O5- 8V + (O8I)). The soft part of the EPIC spectrum of this system is thermal with typical temperatures of about 2 x 106 to 9 x 106 K. The nature ( thermal vs. non-thermal) of the hard part of the spectrum is not unambiguously revealed by our data. If the emission is thermal, the high temperature of the plasma (similar to 2.3 x 10(7) to 4.6 x 10(7) K) would be typical of what should be expected from a wind-wind interaction zone within a long period binary system. This emission could arise from an interaction between the combined winds of the O5- 8V + O5- 8V close binary system and that of the more distant O8I companion. Assuming instead that the hard part of the spectrum is non-thermal, the photon index would be rather steep (similar to 3). Moreover, a marginal variability between our two XMM-Newton pointings could be attributed to an eclipse of the O5 - 8V + O5 - 8V system. The overall X-ray luminosity points to a significant X-ray luminosity excess of about a factor 4 possibly due to colliding winds. Considering HD 167971 along with several recent X-ray and radio observations, we propose that the simultaneous observation of non-thermal radiation in the X-ray (below 10.0 keV) and radio domains appears rather unlikely. Our investigation of our XMM-Newton data of NGC 6604 reveals a rather sparse distribution of X-ray emitters. Including the two bright non-thermal radio emitters HD 168112 and HD 167971, we present a list of 31 X-ray sources along with the results of the cross-correlation with optical and infrared catalogues. A more complete spectral analysis is presented for the brightest X-ray sources. Some of the members of NGC 6604 present some characteristics suggesting they may be pre-main sequence star candidates. [less ▲]

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See detailNon-thermal radio emission from O-type stars. I. HD168112
Blomme, Ronny; Van Loo, S.; De Becker, Michaël ULg et al

in Astronomy and Astrophysics (2005), 436(3), 1033-1040

We present a radio lightcurve of the O5.5 III(f(+)) star HD 168112, based on archive data from the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). The fluxes show considerable ... [more ▼]

We present a radio lightcurve of the O5.5 III(f(+)) star HD 168112, based on archive data from the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). The fluxes show considerable variability and a negative spectral index, thereby confirming that HD 168112 is a non-thermal radio emitter. The non-thermal radio emission is believed to be due to synchrotron radiation from relativistic electrons that have been Fermi accelerated in shocks. For HD 168112, it is not known whether these shocks are due to a wind-wind collision in a binary system or to the intrinsic instability of the stellar wind driving mechanism. Assuming HD 168112 to be a single star, our synchrotron model shows that the velocity jump of the shocks should be very high, or there should be a very large number of shocks in the wind. Neither of these is compatible with time-dependent hydrodynamical calculations of O star winds. If, on the other hand, we assume that HD 168112 is a binary, the high velocity jump is easily explained by ascribing it to the wind-wind collision. By further assuming the star to be an eccentric binary, we can explain the observed radio variability by the colliding-wind region moving in and out of the region where free-free absorption is important. The radio data presented here show that the binary has a period of between one and two years. By combining the radio data with X-ray data, we find that the most likely period is similar to 1.4 yr. [less ▲]

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See detailOptical spectroscopy of X-Mega targets - V. The spectroscopic binary HD 93161 A and its visual companion HD 93161 B
Nazé, Yaël ULg; Antokhin, I. I.; Sana, H. et al

in Monthly Notices of the Royal Astronomical Society (2005), 359(2), 688-698

We present the analysis of an extensive set of high-resolution spectroscopic observations of HD 93161, a visual binary with a separation of 2 arcsec. HD 93161 A is a spectroscopic binary, with both ... [more ▼]

We present the analysis of an extensive set of high-resolution spectroscopic observations of HD 93161, a visual binary with a separation of 2 arcsec. HD 93161 A is a spectroscopic binary, with both components clearly detected throughout the orbit. The primary star is most probably of spectral type O8V, while the secondary is likely an O9V. We obtain the first orbital solution for this system, characterized by a period of 8.566 +/- 0.004 d. The minimum masses of the primary and secondary stars are 22.2 +/- 0.6 and 17.0 +/- 0.4 M-., respectively. These values are quite large, suggesting a high inclination of the orbit. The second object, HD 93161 B, displays an O6.5V(f) spectral type and is thus slightly hotter than its neighbour. This star is at first sight single but presents radial velocity variations. Finally, we study HD 93161 in the X-ray domain. No significant variability is detected. The X-ray spectrum is well described by a 2T model with kT(1) similar to 0.3 keV and kT(2) similar to 0.7 keV. The X-ray luminosity is rather moderate, without any large emission excess imputable to a wind interaction. [less ▲]

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See detailThe spectrum of the very massive binary system WR20a (WN6ha+WN6ha): Fundamental parameters and wind interactions
Rauw, Grégor ULg; Crowther, P. A.; De Becker, Michaël ULg et al

in Astronomy and Astrophysics (2005), 432(3), 985-998

We analyse the optical spectrum of the very massive binary system WR20a (WN6ha + WN6ha). The most prominent emission lines, Halpha and He II lambda4686, display strong phase-locked profile variability ... [more ▼]

We analyse the optical spectrum of the very massive binary system WR20a (WN6ha + WN6ha). The most prominent emission lines, Halpha and He II lambda4686, display strong phase-locked profile variability. From the variations of their equivalent widths and from a tomographic analysis, we find that part of the line emission probably arises in a wind interaction region between the stars. Our analysis of the optical spectrum of WR20a indicates a reddening of A(nu) similar or equal to 6.0 mag and a distance of similar to 7.9 kpc, suggesting that the star actually belongs to the open cluster Westerlund 2. The location of the system at similar to 1.1 pc from the cluster core could indicate that WR20a was gently ejected from the core via dynamical interactions. Using a non-LTE model atmosphere code, we derive the fundamental parameters of each component: T-eff = 43 000 +/- 2000 K, log L-bol/ L-. similar or equal to 6.0, (M) over dot = 8.5 x 10(-6) M-. yr(-1) (assuming a clumped wind with a volume filling factor f = 0.1). Nitrogen is enhanced in the atmospheres of the components of WR20a, while carbon is definitely depleted. Finally, the position of the binary components in the Hertzsprung-Russell diagram suggests that they are core hydrogen burning stars in a pre-LBV stage and their current atmospheric chemical composition probably results from rotational mixing that might be enhanced in a close binary compared to a single star of same age. [less ▲]

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See detailOn the multiplicity of the O-star Cyg OB2#8a and its contribution to the gamma-ray source 3EG J2033+4118
De Becker, Michaël ULg; Rauw, Grégor ULg; Swings, Jean-Pierre ULg

in Astrophysics & Space Science (2005), 297(1-4), 291-298

We present the results of an intensive spectroscopic campaign in the optical waveband revealing that Cyg OB2 # 8A is an O6+ O5.5 binary system with a period of about 21.9 days. Cyg OB2 # 8A is a bright X ... [more ▼]

We present the results of an intensive spectroscopic campaign in the optical waveband revealing that Cyg OB2 # 8A is an O6+ O5.5 binary system with a period of about 21.9 days. Cyg OB2 # 8A is a bright X-ray source, as well as a non-thermal radio emitter. We discuss the binarity of this star in the framework of a campaign devoted to the study of non-thermal emitters, from the radio waveband to gamma-rays. In this context, we attribute the non-thermal radio emission from this star to a population of relativistic electrons, accelerated by the shock of the wind-wind collision. These relativistic electrons could also be responsible for a putative gamma-ray emission through inverse Compton scattering of photospheric UV photons, thus contributing to the yet unidentified EGRET source 3EG J2033+ 4118. [less ▲]

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See detailAn XMM-Newton look at the Wolf-Rayet star WR 40 - The star itself, its nebula and its neighbours
Gosset, Eric ULg; Nazé, Yaël ULg; Claeskens, Jean-François ULg et al

in Astronomy and Astrophysics (2005), 429(2), 685-704

We present the results of an XMM-Newton observation of the field of the Wolf-Rayet star WR 40. Despite a nominal exposure of 20 ks and the high sensitivity of the satellite, the star itself is not ... [more ▼]

We present the results of an XMM-Newton observation of the field of the Wolf-Rayet star WR 40. Despite a nominal exposure of 20 ks and the high sensitivity of the satellite, the star itself is not detected: we thus derive an upper limit on its X-ray flux and luminosity. Joining this result to recent reports of a non-detection of some WC stars, we suggest that the X-ray emission from single normal Wolf-Rayet stars could often be insignificant despite remarkable instabilities in the wind. On the basis of a simple modelling of the opacity of the Wolf-Rayet wind of WR 40, we show that any X-ray emission generated in the particular zone where the shocks are supposed to be numerous will indeed have little chance to emerge from the dense wind of the Wolf-Rayet star. We also report the non-detection of the ejecta nebula RCW 58 surrounding WR 40. Concerning the field around these objects, we detected 33 X-ray sources, most of them previously unknown: we establish a catalog of these sources and cross-correlate it with catalogs of optical/infrared sources. [less ▲]

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See detailA period and a prediction for the Of ? p spectrum alternator HD 191612
Walborn, Nolan R.; Howarth, Ian D.; Rauw, Grégor ULg et al

in Astrophysical Journal (2004), 617(1, Part 2), 61-64

The observational picture of the enigmatic O-type spectrum variable HD 191612 has been sharpened substantially. A symmetrical, low-amplitude light curve with a period near 540 days has recently been ... [more ▼]

The observational picture of the enigmatic O-type spectrum variable HD 191612 has been sharpened substantially. A symmetrical, low-amplitude light curve with a period near 540 days has recently been reported from Hipparcos photometry. This period satisfies all of the spectroscopy since at least 1982, including extensive new observations during 2003 and 2004, and it has predicted the next transition during 2004 September - October. Measurements of the Ha equivalent width reveal a sharp emission peak in the phase diagram, in contrast to the apparently sinusoidal light curve. The He II absorption-line strength is essentially constant, while He I varies strongly, possibly filled in by emission in the O6 state, thus producing the apparent spectral type variations. The O8 state appears to be the "normal" one. Two intermediate O7 observations have been obtained, which fall at the expected phases, but these are the only modern observations of the transitions so far. The period is too long for rotation or pulsation; although there is no direct evidence as yet for a companion, a model in which tidally induced oscillations drive an enhanced wind near periastron of an eccentric orbit appears promising. Further observations during the now predictable transitions may provide a critical test. Ultraviolet and X-ray observations during both states will likely also prove illuminating. [less ▲]

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See detailLine profile variability in the spectra of Oef stars - II. HD192281, HD14442 and HD14434
De Becker, Michaël ULg; Rauw, Grégor ULg

in Astronomy and Astrophysics (2004), 427(3), 995-1008

We present the very first analysis of the spectroscopic variability of the three rapidly rotating Oef stars HD 192281 (O5(ef)), HD14442 (O5.5ef) and HD 14434 (O6.5( ef)). Radial velocities of the He II ... [more ▼]

We present the very first analysis of the spectroscopic variability of the three rapidly rotating Oef stars HD 192281 (O5(ef)), HD14442 (O5.5ef) and HD 14434 (O6.5( ef)). Radial velocities of the He II lambda 4541 line reveal no evidence of binarity on time scales of a few days, or from one year to the next, for any of the targets. The He II lambda 4686 double-peaked emission and, to some extent, the H absorption line display significant profile variability in the spectra of all three stars. Data gathered during different observing runs spread over six years reveal a rather stable time scale for HD 192281 and HD14442, whereas the variability pattern changes significantly from one year to the other. The case of HD 14434 is less clear as no obvious time scale emerges from our analysis. In a tentative way to interpret this variability, stellar rotation remains a possible clock for HD 192281 and HD14442. However, currently available models addressing stellar rotation fail to explain some crucial aspects of the observed variability behaviour, which appear to be even more complex in the case of HD 14434. [less ▲]

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See detailHard X-ray emission clumps in the gamma-Cygni supernova remnant: An INTEGRAL-ISGRI view
Bykov, A. M.; Krassilchtchikov, A. M.; Uvarov, Y. A. et al

in Astronomy and Astrophysics (2004), 427(3), 21-24

Spatially resolved images of the galactic supernova remnant G78.2+2.1 (gamma-Cygni) in hard X-ray energy bands from 25 keV to 120 keV are obtained with the IBIS-ISGRI imager aboard the International Gamma ... [more ▼]

Spatially resolved images of the galactic supernova remnant G78.2+2.1 (gamma-Cygni) in hard X-ray energy bands from 25 keV to 120 keV are obtained with the IBIS-ISGRI imager aboard the International Gamma-Ray Astrophysics Laboratory INTEGRAL. The images are dominated by localized clumps of about ten arcmin in size. The flux of the most prominent North-Western (NW) clump is (1.7+/-0.4)x10(-11) erg cm(-2) s(-1) in the 25-40 keV band. The observed X-ray fluxes are in agreement with extrapolations of soft X-ray imaging observations of gamma-Cyg by ASCA GIS and spatially unresolved RXTE PCA data. The positions of the hard X-ray clumps correlate with bright patches of optical line emission, possibly indicating the presence of radiative shock waves in a shocked cloud. The observed spatial structure and spectra are consistent with model predictions of hard X-ray emission from nonthermal electrons accelerated by a radiative shock in a supernova interacting with an interstellar cloud, but the powerful stellar wind of the O9V star HD 193322 is a plausible candidate for the NW source as well. [less ▲]

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See detailNon-thermal emission from early-type binaries
Rauw, Grégor ULg

in Cosmic Gamma-Ray Sources (2004)

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See detailA spectroscopic study of the non-thermal radio emitter Cyg OB2#8A: Discovery of a new binary system
De Becker, Michaël ULg; Rauw, Grégor ULg; Manfroid, Jean ULg

in Astronomy and Astrophysics (2004), 424(3), 39-42

We present the results of a spectroscopic campaign revealing that the non-thermal radio emitter Cyg OB2 #8A is an O6+O5.5 binary system. We propose the very first orbital solution indicating a period of ... [more ▼]

We present the results of a spectroscopic campaign revealing that the non-thermal radio emitter Cyg OB2 #8A is an O6+O5.5 binary system. We propose the very first orbital solution indicating a period of about 21.9 days. The system appears to be eccentric (0.24+/-0.04) and is likely seen under a rather low inclination angle. The mass ratio of the components is close to unity. The impact of the binarity of this star in the framework of our understanding of non-thermal radio emission from early-type stars is briefly discussed. [less ▲]

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See detailEarly-type stars in the young open cluster IC 1805 - I. The SB2 system BD+60 degrees 497 and the probably single stars BD+60 degrees 501 and BD+60 degrees 513
Rauw, Grégor ULg; De Becker, Michaël ULg

in Astronomy and Astrophysics (2004), 421(2), 693-702

We investigate the multiplicity of three O-type stars in the very young open cluster IC 1805. All our targets were previously considered as spectroscopic binaries, but no orbital solution was available ... [more ▼]

We investigate the multiplicity of three O-type stars in the very young open cluster IC 1805. All our targets were previously considered as spectroscopic binaries, but no orbital solution was available for any of them. Our results confirm the binarity of BD+60degrees 497 and we provide the very first orbital solution for this double-lined spectroscopic binary. This is only the second O-star binary in IC 1805, and the first SB2 system, for which an orbital solution is now available. BD+60degrees 497 has an orbital period of 3.96 days and consists of an evolved 06.5 V((f)) primary and an 08.5-9.5 V((f)) secondary with minimum masses of m, sin(3) i = 13.9 M-circle dot and m(2) sin 3 i = 10.9 M-circle dot. The observed primary/secondary mass ratio (1.28) appears lower than expected from a comparison with single star evolutionary models (1.60-1.74). For the other two stars, BD+60degrees 501 and BD+60degrees 513, we find no significant radial velocity variations, suggesting that they are most probably single. Although a fraction of binaries among the early-type stars of IC 1805 as high as 80% has been advocated in the literature, our results suggest that this number might be overestimated. [less ▲]

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See detailQuasi-simultaneous XMM-Newton and VLA observation of the non-thermal radio emitter HD 168112 (O5.5III(f+))
De Becker, Michaël ULg; Rauw, Grégor ULg; Blomme, Ronny et al

in Astronomy and Astrophysics (2004), 420

We report the results of a multiwavelength study of the non-thermal radio emitter HD 168112 (O5.5III(f+)). The detailed analysis of two quasi-simultaneous XMM-Newton and VLA observations reveals strong ... [more ▼]

We report the results of a multiwavelength study of the non-thermal radio emitter HD 168112 (O5.5III(f+)). The detailed analysis of two quasi-simultaneous XMM-Newton and VLA observations reveals strong variability of this star both in the X-ray and radio ranges. The X-ray observations separated by five months reveal a decrease of the X-ray flux of ˜30%. The radio emission on the other hand increases by a factor 5-7 between the two observations obtained roughly simultaneously with the XMM-Newton pointings. The X-ray data reveal a hard emission that is most likely produced by a thermal plasma at kT ˜ 2-3 keV while the VLA data confirm the non-thermal status of this star in the radio waveband. Comparison with archive X-ray and radio data confirms the variability of this source in both wavelength ranges over a yet ill defined time scale. The properties of HD 168112 in the X-ray and radio domain point towards a binary system with a significant eccentricity and an orbital period of a few years. However, our optical spectra reveal no significant changes of the star's radial velocity suggesting that if HD 168112 is indeed a binary, it must be seen under a fairly low inclination. [less ▲]

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See detailWR 20a: A massive cornerstone binary system comprising two extreme early-type stars
Rauw, Grégor ULg; De Becker, Michaël ULg; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2004), 420(2), 9-13

We analyse spectroscopic observations of WR20a revealing that this star is a massive early-type binary system with a most probable orbital period of similar to3.675 days. Our spectra indicate that both ... [more ▼]

We analyse spectroscopic observations of WR20a revealing that this star is a massive early-type binary system with a most probable orbital period of similar to3.675 days. Our spectra indicate that both components are most likely of WN6ha or 031f*/WN6ha spectral type. The orbital solution for a period of 3.675 days yields extremely large minimum masses of 70.7 +/- 4.0 and 68.8 +/- 3.8 M. for the two stars. These properties make WR 20a a cornerstone system for the study of massive star evolution. [less ▲]

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