Extreme Ultraviolet Explorer Optical Identification Campaign.III. A Southern Hemisphere Sample of Active Late-Type Stars and White Dwarfs

Craig, N.; Christian, D. J.; Dupuis, J.; Roberts, Bryce

doi:10.1086/118469

Cited by 10 publications

(7 citation statements)

References 16 publications

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“…Table 1 lists their observed and derived quantities. Some of these have been identified by previous surveys (Carpenter et al 2001, Craig et al 1997, Fuhrmeister et al 2003, Koehler 2001, Li et al 1998, Li et al 2000, MacConnell 1981, Massey 2002, Preibisch et al 1999, Thompson et al 1998, Zickgraf et al 2003. In principle, some giants could be included in our sample, but as discussed in Section 5.1, the spectra for none of these classify them as giants.…”

Section: Sample Selectionmentioning

confidence: 86%

Identification of New M Dwarfs in the Solar Neighborhood

2006

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We present the results from a spectroscopic study of 1080 nearby active M dwarfs, selected by correlating the 2MASS and ROSAT catalogs. We have derived the spectral types and estimated distances for all of our stars. The spectral types range between K5 and M6. Nearly half of our stars lie within 50 pc. We have measured the equivalent width of the H alpha emission line. Our targets show an increase in chromospheric activity from early to mid-spectral types, with a peak in activity around M5. Using the count rate and hardness ratios obtained from the ROSAT catalog, we have derived the X-ray luminosities. Our stars display a "saturation-type" relation between the chromospheric and coronal activity. The relation is such that log (Lx/Lbol) remains "saturated" at a value of about -3 for varying H alpha equivalent width. We have found 568 matches in the USNO-B catalog, and have derived the tangential velocities for these stars. There is a slight trend of decreasing chromospheric activity with age, such that the stars with higher Vtan have lower H alpha equivalent widths. The coronal emission, however, remains saturated at a value of log (Lx/Lbol) -3 for varying tangential velocities, suggesting that the coronal activity remains saturated with age. We do not find any break in the saturation-type relation at the spectral type where stars become fully convective (~M3.5). Most of the stars in our sample show more coronal emission than the dMe stars in the Hyades and Praesepe clusters, and have Vtan< 40km/s, suggesting a young population.Comment: 24 pages, 8 figures, accepted for publication on A

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Section: Sample Selectionmentioning

confidence: 86%

Identification of New M Dwarfs in the Solar Neighborhood

2006

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“…10 Note that in the case of CD −33 • 7795, it could be argued that there is no detection because there is no disk: this source does not show infrared excess (Jayawardhana et al 1999;Weinberger et al 2004;Uchida et al 2004). However the source does exhibit Hα in emission Craig et al (1997) and U − V excess. Table 4.…”

Section: H 2 Nir Ro-vibrational Emission In Lkhα 264 and Other T Taurmentioning

confidence: 90%

“…(8) Ramsay Howat & Greaves (2007). Notes: † M disk refers to the total mass in the disk deduced from mm dust continuum emission assuming a gas to dust ratio of 100. a Average value from Table 5 of Bary et al (2003); b spectral type, Hα EW and A V from Cohen & Kuhi (1979); c Varsavsky (1960); d average between the excess of the two spectral types; e Neuhäuser et al (1995); f Mendoza (1966); g Bastian & Mundt (1979); h Hα EW by Herbig & Bell (1988); ha given the Hα EW we classified the source as CTTS; i Herbig & Bell (1988); j quadruple system (Soderblom et al 1998); k Mermilliod (1986); l XEST data by Güdel et al (2007); m Craig et al (1997); (2007); y ROTOR data (Grankin et al 2007) gives an E(B − V) of −0.74 which is more than a magnitude off from that of Herbig & Bell (1988). Maybe there is some long-term evolution of this system that changes its colors on a long time scale.…”

Section: H 2 Nir Ro-vibrational Emission In Lkhα 264 and Other T Taurmentioning

confidence: 99%

A search for near-infrared molecular hydrogen emission in the CTTS LkH$\mathsf{\alpha}$ 264 and the debris disk 49 Ceti

Ancker

Henning

Goto

et al. 2007

A&A

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We report on the first results of a search for molecular hydrogen emission from protoplanetary disks using CRIRES, ESO's new VLT Adaptive Optics high resolution near-infrared spectrograph. We observed the classical T Tauri star LkHα 264 and the debris disk 49 Cet, and searched for υ = 1−0 S(1) H 2 emission at 2.1218 µm, υ = 1−0 S(0) H 2 emission at 2.2233 µm and υ = 2−1 S(1) H 2 emission at 2.2477 µm. The H 2 line at 2.1218 µm is detected in LkHα 264 confirming the previous observations by Itoh et al. (2003). In addition, our CRIRES spectra reveal the previously observed but not detected H 2 line at 2.2233 µm in LkHα 264. An upper limit of 5.3 ×10 −16 erg s −1 cm −2 on the υ = 2−1 S(1) H 2 line flux in LkHα 264 is derived. The detected lines coincide with the rest velocity of LkHα 264. They have a FWHM of ∼20 km s −1 . This is strongly suggestive of a disk origin for the lines. These observations are the first simultaneous detection of υ = 1−0 S(1) and υ = 1−0 S(0) H 2 emission from a protoplanetary disk. 49 Cet does not exhibit H 2 emission in any of the three observed lines. We derive the mass of optically thin H 2 at T ∼ 1500 K in the inner disk of LkHα 264 and derive stringent limits in the case of 49 Cet at the same temperature. There are a few lunar masses of optically thin hot H 2 in the inner disk (∼0.1 AU) of LkHα 264, and less than a tenth of a lunar mass of hot H 2 in the inner disk of 49 Cet. The measured 1−0 S(0)/1−0 S(1) and 2−1 S(1)/1−0 S(1) line ratios in LkHα 264 indicate that the H 2 emitting gas is at a temperature lower than 1500 K and that the H 2 is most likely thermally excited by UV photons. The υ = 1−0 S(1) H 2 line in LkHα 264 is single peaked and spatially unresolved. Modeling of the shape of the line suggests that the disk should be seen close to face-on (i < 35 • ) and that the line is emitted within a few AU of the LkHα 264 disk. A comparative analysis of the physical properties of classical T Tauri stars in which the H 2 υ = 1−0 S(1) line has been detected and non-detected indicates that the presence of H 2 emission is correlated with the magnitude of the UV excess and the strength of the Hα line. The lack of H 2 emission in the NIR spectra of 49 Cet and the absence of Hα emission suggest that the gas in the inner disk of 49 Cet has dissipated. These results combined with previous detections of 12 CO emission at sub-mm wavelengths indicate that the disk surrounding 49 Cet should have an inner hole. We favor inner disk dissipation by inside-out photoevaporation, or the presence of an unseen low-mass companion as the most likely explanations for the lack of gas in the inner disk of 49 Cet.

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“…Previous optical studies of late-type stars selected from EUV and soft X-ray surveys detections have shown strong chromospheric emission lines. These include follow-up studies of ROSAT WFC (e.g., Jeffries & Jewell 1993) and EUVE sources (Craig et al 1995(Craig et al , 1997Polomski et al 1997;Christian et al 2001). Our late-type star sample shows strong Balmer and He i emission lines.…”

Section: Chromospheric Activity Indicatorsmentioning

confidence: 92%

High-Resolution Optical Observations of Extreme-Ultraviolet–selected Active Late-Type Stars

Christian

Mathioudakis

2002

The Astronomical Journal

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We present high-resolution optical spectra of EUV-selected late-type stars. We have detected seven new spectroscopic binaries, including a pair of F stars and an RS Canum Venaticorum candidate. Many of the stars in our sample show remarkable H emission with equivalent widths up to 8 A ˚. Several sources show strong He i 5876 A ˚emission. We use cross-correlation techniques to estimate line-of-sight rotational velocities and find that they range from less than 5 to over 80 km s À1 . Several of the stars show a strong Li 6707 A line, which we use to determine their Li abundances. The EUV-to-bolometric luminosity, a measure of the coronal heating efficiency, is as high as 10 À3 . The present sample extends the EUV-selected late-type stars to lower Rossby numbers and makes the coronal saturation boundary better pronounced. Our results indicate that there is a drop in the EUV emission from the corona in late M dwarfs possibly because of a change in the nature of the magnetic dynamo in fully convective stars.

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Extreme Ultraviolet Explorer Optical Identification Campaign.III. A Southern Hemisphere Sample of Active Late-Type Stars and White Dwarfs

Cited by 10 publications

References 16 publications

Identification of New M Dwarfs in the Solar Neighborhood

Identification of New M Dwarfs in the Solar Neighborhood

A search for near-infrared molecular hydrogen emission in the CTTS LkH$\mathsf{\alpha}$ 264 and the debris disk 49 Ceti

High-Resolution Optical Observations of Extreme-Ultraviolet–selected Active Late-Type Stars

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