Picornaviruses: Classification of Nine New Types

Melnick, Joseph L.; Chanock, Robert M.; Gelfand, Henry M.; Hammon, William McD.; Huebner, Robert J.; Rosen, Léon; Sabin, Albert B.; Wenner, Herbert A.

doi:10.1126/science.141.3576.153

Cited by 41 publications

(29 citation statements)

References 8 publications

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“…Stellar temperatures (T eff ) of OB stars are taken from Crowther (1997b), with determinations of luminosities (L), ionizing fluxes (Q 0 ) and mass-loss rates (Ṁ) described in Section 7. References: (a) Melnick (1985); (b) Parker (1993); (c) Walborn & Blades (1997); (d) Massey & Hunter (1997); (e) this work a lower age limit of 2.7-3.5 Myr (at Z ¼ 0.02) for the appearance of a WNL star with progenitor mass of 60-85 M ᭪ . Hofmann et al (1995) argue for an age of 3.2 Myr for NGC 3603, with younger ages excluded on the basis that they would require extremely high initial masses (Ն 120 M ᭪ ) for the WR stars.…”

Section: Cluster Agesmentioning

confidence: 84%

“…This sample has been drawn from the catalogues of Parker (1993), and Hunter et al (1995). Additional spectral classifications have been provided by Melnick (1985), Walborn & Blades (1997) and Massey & Hunter (1998). We include our own spectral classifications of several O stars in the vicinity of R136a, that were observed with HST FOS during 1996 (P. I. Heap).…”

Section: Stellar Populationsmentioning

confidence: 99%

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Quantitative spectroscopy of Wolf—Rayet stars in HD 97950 and R136a — the cores of giant H ii regions

Crowther¹,

Dessart²

1998

Monthly Notices of the Royal Astronomical Society

156

218

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We present quantitative analyses of Wolf–Rayet stars in the cores of two giant H ii regions — HD 97950 in NGC 3603 and R136a in 30 Doradus — based on archive Hubble Space Telescope (HST) spectroscopy. We confirm previous WN6h+abs classifications for components A1, B and C in HD 97950, while classifications for R136a1–3 are revised from O3 If*/WN6 to WN5h. From detailed non‐local thermodynamic equilibrium analyses, we find that all Wolf–Rayet stars exhibit products of CNO‐processed material at their surface since they are rich in both helium (H/He ≈ 3–6, by number) and nitrogen (N/He ≈ 0.002–0.006). Their luminosities, log (L/L⊙) = 6.0–6.3, are amongst the highest known for Wolf–Rayet stars. Consequently they are very massive stars (Minit ≥ 100 M⊙) at a relatively low age (∼ 2 Myr), reminiscent of the late WN stars in the Carina Nebula. We obtain a revised distance modulus of 15.03 mag (= 10.1 kpc) to NGC 3603 based on available photometry, an updated Mv calibration for early O stars and a reddening of E (B − V) = 1.23 mag towards its core. From a census of the massive stellar content of the two central clusters we conclude that their global properties are comparable. We evaluate the contribution made by Wolf–Rayet stars to the total Lyman continuum ionizing flux and kinetic energy released into the ISM. We discuss how simple calibrations can be used to estimate stellar luminosities, ionizing fluxes and mass‐loss rates of luminous OB stars. Wolf–Rayet stars provide ∼ 20 per cent of the total ionizing flux (∼ 1.3 × 1051 Ly photon s−1) within 0.5 pc of their cores, and ∼ 60 per cent of the total kinetic energy injected into the ISM (5–6 × 1038 erg s−1), despite representing only 10 per cent of the massive stellar population. For the larger R136 cluster in 30 Doradus (r ≤ 10 pc), 117 massive stars provide a total ionizing flux of 4 × 1051 Ly photon s−1 and release a total kinetic energy of 1.6 × 1039 erg s−1 into the ISM, the latter being dominated by nine WR (43 per cent) and six O3 If*/WN (29 per cent) stars.

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Section: Cluster Agesmentioning

confidence: 84%

Section: Stellar Populationsmentioning

confidence: 99%

Quantitative spectroscopy of Wolf—Rayet stars in HD 97950 and R136a — the cores of giant H ii regions

Crowther¹,

Dessart²

1998

Monthly Notices of the Royal Astronomical Society

156

218

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“…This nebulosity can also be seen in the NICMOS image from Brandner et al (2001, their 30Dor-NIC01 frame), but did not feature in their discussion. 3 We note the candidate YSO '30 Dor-22' from Kim et al (2007) is, on the basis of their published astrometry, Mk 34 (Melnick 1985), a well-studied WN star. We are puzzled that Kim et al mention this as one of the sources studied by Brandner et al (2001), as it does not feature in their NICMOS fields.…”

Section: 35−6906304mentioning

confidence: 99%

VLT-MAD observations of the core of 30 Doradus

Campbell

Evans

Mackey

et al. 2010

Monthly Notices of the Royal Astronomical Society

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We present H- and Ks-band imaging of three fields at the centre of 30 Doradus in the Large Magellanic Cloud, obtained as part of the Science Demonstration programme with the Multi-conjugate Adaptive optics Demonstrator (MAD) at the Very Large Telescope. Strehl ratios of 15-30% were achieved in the Ks-band, yielding near-infrared images of this dense and complex region at unprecedented angular resolution at these wavelengths. The MAD data are used to construct a near-infrared luminosity profile for R136, the cluster at the core of 30 Dor. Using cluster profiles of the form used by Elson et al., we find the surface brightness can be fit by a relatively shallow power-law function (gamma~1.5-1.7) over the full extent of the MAD data, which extends to a radius of ~40" (~10pc). We do not see compelling evidence for a break in the luminosity profile as seen in optical data in the literature, arguing that cluster asymmetries are the dominant source, although extinction effects and stars from nearby triggered star-formation likely also contribute. These results highlight the need to consider cluster asymmetries and multiple spatial components in interpretation of the luminosity profiles of distant unresolved clusters. We also investigate seven candidate young stellar objects reported by Gruendl & Chu from Spitzer observations, six of which have apparent counterparts in the MAD images. The most interesting of these (GC09: 053839.24-690552.3) appears related to a striking bow-shock--like feature, orientated away from both R136 and the Wolf-Rayet star Brey 75, at distances of 19.5" and 8" (4.7 and 1.9pc in projection), respectively

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“…The spectral type O3If*/WN6-A was introduced almost 30 years ago by Walborn (1982) to classify the bright emission line star Sk-67 22 in the LMC, which shows an intermediate spectrum between those of HD93129A (O2 If*) and HD93162 (=WR25, Melnick 1985;Walborn & Blades 1997;.…”

Section: Introductionmentioning

confidence: 99%

Two O2 If*/WN6 stars possibly ejected from the massive young Galactic cluster Westerlund 2

Roman-Lopes¹,

Barbá²,

Morrell³

2011

Monthly Notices of the Royal Astronomical Society

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In this paper we report the identification of two new Galactic O2 If*/WN6 stars (WR20aa and WR20c), on the outskirts of the massive young stellar cluster Westerlund 2. The morphological similarity between the near‐infrared spectra of the new stars with that of WR20a and WR21a (two of the most massive binaries known to date) is remarkable, indicating that probably they are also very massive stars. New optical spectroscopic observations of WR20aa suggest an intermediate O2 If*/WN6 spectral type. Based on a mosaic made from the 3.6 μm Spitzer IRAC images of the region including part of the RCW49 complex, we studied the spatial location of the new emission line stars, finding that WR20aa and WR20c are well displaced from the centre of Westerlund 2, being placed at ≈36 pc (15.7 arcmin) and ≈58 pc (25.0 arcmin), respectively, for an assumed heliocentric distance of 8 kpc. Also, very remarkably, a radius vector connecting the two stars would intercept the Westerlund 2 cluster exactly at the place where its stellar density reaches a maximum. We consequently postulate a scenario in which WR20aa and WR20c had a common origin somewhere in the cluster core, being ejected from their birthplace by dynamical interaction with some other very massive objects, perhaps during some earlier stage of the cluster evolution.

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Picornaviruses: Classification of Nine New Types

Cited by 41 publications

References 8 publications

Quantitative spectroscopy of Wolf—Rayet stars in HD 97950 and R136a — the cores of giant H ii regions

Quantitative spectroscopy of Wolf—Rayet stars in HD 97950 and R136a — the cores of giant H ii regions

VLT-MAD observations of the core of 30 Doradus

Two O2 If*/WN6 stars possibly ejected from the massive young Galactic cluster Westerlund 2

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