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Register a new userThe First Optical Spectra of Wolf Rayet Stars in M101 Revealed with Gemini/GMOS
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Deep narrow-band HST imaging of the iconic spiral galaxy M101 has revealed over a thousand new Wolf Rayet (WR) candidates. We report spectrographic confirmation of 10 HeII emission line sources hosting 15 WR stars. We find WR stars present at both sub- and super-solar metalicities with WC stars favouring more metal-rich regions compared to WN stars. We investigate the association of WR stars with HII regions using archival HST imaging and conclude that the majority of WR stars are in or associated with HII regions. Of the 10 emission lines sources, only one appears to be unassociated with a star-forming region. Our spectroscopic survey provides confidence that our narrow-band photometric candidates are in fact bonafide WR stars, which will allow us to characterise the progenitors of any core-collapse supernovae that erupt in the future in M101.
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We investigate the influence of Wolf-Rayet (W-R) stars on their surrounding star-forming molecular clouds. We study five regions containing W-R stars in the inner Galactic plane ($lsim$[14$^circ$-52$^circ$]), using multi-wavelength data from near-infrared to radio wavelengths. Analysis of $^{13}$CO line data reveals that these W-R stars have developed gas-deficient cavities in addition to molecular shells with expansion velocities of a few km s$^{-1}$. The pressure owing to stellar winds primarily drives these expanding shells and sweeps up the surrounding matter to distances of a few pc. The column densities of shells are enhanced by a minimum of 14% for one region to a maximum of 88% for another region with respect to the column densities within their central cavities. No active star formation - including molecular condensations, protostars, or ionized gas - is found inside the cavities, whereas such features are observed around the molecular shells. Although the expansion of ionized gas is considered an effective mechanism to trigger star formation, the dynamical ages of the HII regions in our sample are generally not sufficiently long to do so efficiently. Overall, our results hint at the possible importance of negative W-R wind-driven feedback on the gas-deficient cavities, where star formation is quenched as a consequence. In addition, the presence of active star formation around the molecular shells indicates that W-R stars may also assist in accumulating molecular gas, and that they could initiate star formation around those shells.
We analyse the impact that spatial resolution has on the inferred numbers and types of Wolf-Rayet (WR) and other massive stars in external galaxies. Continuum and line images of the nearby galaxy M33 are increasingly blurred to mimic effects of different distances from 8.4Mpc to 30Mpc, for a constant level of seeing. We use differences in magnitudes between continuum and Helium II line images, plus visual inspection of images, to identify WR candidates via their ionized helium excess. The result is a surprisingly large decrease in the numbers of WR detections, with only 15% of the known WR stars predicted to be detected at 30Mpc. The mixture of WR sub-types is also shown to vary significantly with increasing distance (poorer resolution), with cooler WN stars more easily detectable than other subtypes. We discuss how spatial clustering of different subtypes and line dilution could cause these differences and the implications for their ages, this will be useful for calibrating numbers of massive stars detected in current surveys. We investigate the ability of ELT/HARMONI to undertake WR surveys and show that by using adaptive optics at visible wavelengths even the faintest (Mv = -3mag) WR stars will be detectable out to 30Mpc.
The Wolf-Rayet (WR) phenomenon is widespread in astronomy. It involves classical WRs, very massive stars (VMS), WR central stars of planetary nebula CSPN [WRs], and supernovae (SNe). But what is the root cause for a certain type of object to turn into an emission-line star? In this contribution, I discuss the basic aspects of radiation-driven winds that might reveal the ultimate difference between WR stars and canonical O-type stars. I discuss the aspects of (i) self-enrichment via CNO elements, (ii) high effective temperatures Teff, (iii) an increase in the helium abundance Y, and finally (iv) the Eddington factor Gamma. Over the last couple of years, we have made a breakthrough in our understanding of Gamma-dependent mass loss, which will have far-reaching consequences for the evolution and fate of the most massive stars in the Universe. Finally, I discuss the prospects for studies of the WR phenomenon in the highest redshift Ly-alpha and He II emitting galaxies.
We present the analysis of archival Very Large Telescope (VLT) Multi Unit Spectroscopic Explorer (MUSE) observations of the interacting galaxies NGC 4038/39 (a.k.a. the Antennae) at a distance of 18.1 Mpc. Up to 38 young star-forming complexes with evident contribution from Wolf-Rayet (WR) stars are unveiled. We use publicly available templates of Galactic WR stars in conjunction with available photometric extinction measurements to quantify and classify the WR population in each star-forming region, on the basis of its nearly Solar oxygen abundance. The total estimated number of WR stars in the Antennae is 4053 $pm$ 84, of which there are 2021 $pm$ 60 WNL and 2032 $pm$ 59 WC-types. Our analysis suggests a global WC to WN-type ratio of 1.01 $pm$ 0.04, which is consistent with the predictions of the single star evolutionary scenario in the most recent BPASS stellar population synthesis models.
I report the discovery of two new Galactic Wolf-Rayet stars in Circinus via detection of their C, N and He Near-Infrared emission lines, using ESO-NTT-SOFI archival data. The H- and K-band spectra of WR67a and WR67b, indicate that they are Wolf-Rayet stars of WN6h and WC8 sub-types, respectively. WR67a presents a weak-lined spectrum probably reminiscent of young hydrogen rich main-sequence stars such as WR25 in Car OB1 and HD97950 in NGC3603. Indeed, this conclusion is reinforced by the close morphological match of the WR67a H- and K-band spectra with that for WR21a, a known extremely massive binary system. WR67b is probably a non-dusty WC8 Wolf-Rayet star that has a estimated heliocentric distance of 2.7(0.9) kpc, which for its Galactic coordinates, puts the star probably in the near portion of the Scutum-Centaurus arm.
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