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classical t tauri

Fig. Alternatively, ionizing fronts of O-stars are thought to trigger star formation by collapsing molecular clouds (see Elmegreen 2000; Karr, Manoj & Ohashi 2009; Snider et al. Oxford University Press is a department of the University of Oxford. (1976) proposed star formation proceeded east to west through time beginning in NGC 6530 which triggered star formation in the Hourglass nebula. Prisinzano et al. A. R. D. Megeath J. S. (2007) classify 31 of the 95 stars for which they present H α spectra as CTTS (Fig. R. J. Not including the lower limits lead to slightly steeper slope. 9 have comparatively younger ages (t* < 0.8 Myr) than stars having 0.2 M⊙ < M* < 0.6 M⊙, the bulk of whose ages lie between 0.8 and 2 Myr according to the Siess et al. G. A. (2000) median of log |$\skew4\dot{M}_{{\rm acc}}$| = −8.1 M⊙ yr−1. The background is modelled using a sliding median filter over a scale of 15 arcsec. B. van Altena Based on observations collected at the European Southern Observatory Very Large Telescope in programme 177.D-3023(C). J. S. T.

Kley In particular, whether photoevaporation from OB stars in the local environment affects |$\skew4\dot{M}_{{\rm acc}}$| remains an open question (Williams & Cieza 2011). 16. Dominik Calvet The approximate centres of the Hourglass nebula, NGC 6530 cluster, and M8 E region are annotated following Fig. J. R. H. Jeffries Cieza

Small differences in the conversion from the theoretical to the observational plane of the Hertzsprung–Russell diagram may lead to differences in the precision of the interpolated ages. R.

Density distribution of |$\skew4\dot{M}_{{\rm acc}}$| in the complete mass range (top) and in the restricted range 0.35 M⊙ < M* < 0.6 M⊙ (bottom), which contains 135 stars. Distance (d) determinations to NGC 6530 using isochrone fitting provide d = 1250 ± 50 pc (Prisinzano et al.

Jennings Bica 2006) and isochrone fitting (Prisinzano et al. Sung et al. R. A. R. Jester 2007; Mayne et al. selon les recommandations des projets correspondants. L. Natta The structure may be being ionized by the O-type star HD 164536 situated around 1 pc to its south-west, causing the bright rims on the western side of the structure. Wang Please note: Oxford University Press are not responsible for the content or functionality of any supporting materials supplied by the authors. Calvet This fact, along with the multiple signatures of disc accretion are highly suggestive that the vast majority of our candidate CTTS are genuinely accreting. Romaniello

Alves

Our estimations suggest that our sample is clean, and complete to a sufficient degree to estimate the statistical properties of the PMS stars within the Lagoon Nebula. 7 in that paper).

224 (95 per cent) stars in our sample were found to have UKIDSS cross-matches.

Marigo In Fig. Although rapidly spatially varying nebulosity on shorter spatial scales can lead to imprecise sky subtractions. 2007). Girardi L. A. Winston Gottlieb Degl'Innocenti H. Damiani J. Spezzi Zinnecker This is a reasonable assumption for late spectral types (K–M6) which form the majority of our observed sample given the 1.5 mag spread in the (r − i) colour across this spectral range, and a mean (r − i) colour error due to the combination of random photometric noise and extinction uncertainty ≲ 0.15 mag. G. 16), which is why we corroborate our map covering the entire observed stellar mass range with one restricted to 0.35–0.6 M⊙ CTTS, which includes 135 candidates. We find no correlation between the H α FWZI and EWH α. Prisinzano et al. 2009). C. Y. Neglecting that such a change is due to accretion variability it is possible that these stars may be foreground unreddened late-type stars. Harnden Symbols are same as Fig.

N. F. H. The system shows clear evidence of an extensive circumbinary disk. The O-type stars 9 Sgr and H 36 are located to the north-west. (2012) used new H α multislit observations to add a further 16 accreting stars to the sample of Prisinzano et al. (2006). In Fig. Two O-type stars are considered, namely the O4 V type star 9 Sgr, which is thought to be ionizing the central part of the Lagoon Nebula, and responsible for clearing gas in the rift within the NGC 6530 cluster (Tothill et al. N. Hartigan Testi (2011) models. E. Classical T-Tauri stars (CTTS) are low-mass pre-main-sequence (PMS) stars thought to accrete mass from a circumstellar disc via a stellar magnetosphere. The diagnostic power of the helium lines lies in their high-excitation potentials, which restrict their formation to a region either of high temperature or close proximity to a source of ionizing radiation. For these stars, age estimates represent an upper limit. Lawson Prada Moroni It is important to consider the observational selection effects that may affect the observed relation (Clarke & Pringle 2006; Da Rio et al. M. S. Tognelli E. We therefore welcome further comparisons of the photometric EWH α with spectroscopic measurements, particularly from future large surveys such as the GAIA-ESO Survey (GES). Y. Vink 2014). John Kwan, University of Massachusetts Amherst. Selon ces chercheurs, il serait creusé par une planète de la masse de Jupiter. We estimate the accretion rates of 235 Classical T Tauri star (CTTS) candidates in the Lagoon Nebula using ugri H α photometry from the VST Photometric H α survey+. In one outburst the \caII IR lines brighten by a factor of 5. 10(a) shows the luminosity function of our sample. The distribution of CTTS is a continuum ranging from dense clustering to relative isolation. The gravity derived for T Tau N $\log{g}=3.45 \pm 0.14$ is lower than the gravity of nearly every other star in a sample of 24 classical T Tauri stars in Taurus.

E. Elles sont toujours situées auprès des nuages moléculaires et caractérisées par des variations brusques et imprévisibles de leur magnitude apparente. S. Affer L. Observations also reveal that |$\skew4\dot{M}_{{\rm acc}}$| scales steeply to the square of the stellar mass M* (Muzerolle et al. The sample of selected CTTS does not include stars that have not met these criteria. E. 22 indicates that the number density of CTTS within 1 pc of 9 Sgr is considerably higher, with the Spearmans ρ = −0.72. 13(a), the (J − H) versus (H − K) colour–colour diagram of stars located in the Lagoon Nebula is plotted. H. L.

The majority of new CTTS are identified at r < 17 mag, beyond the limiting magnitude of Sung et al. S. 9).

Martín C. Kroupa 2000) to the whole CTTS population within the region) follows a similar trend, with the disc fraction somewhat smaller within 1 pc but steady thereafter until beyond 5 pc. (2007) to suggest the possibility of Bondi–Hoyle or competitive accretion in protostars in such regions due to the possibility of overlapping envelopes. In the resulting sample, 12 384 sources have riH α photometry. D. Sicilia-Aguilar Observations used in this paper are detailed in Table 1.

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