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Meeting the Cool Neighbors. XI. Beyond the NLTT Catalog
We have combined near-infrared data from the Two Micron All Sky Surveywith ancillary optical data to identify previously unrecognizedproper-motion stars that have colors and magnitudes consistent withnearby M dwarfs. We present follow-up observations of 392 stars fromthat sample, including ~200 stars discussed here for the first time. Ourdistance estimates, based primarily on spectroscopic parallaxes, place123 stars within 20 pc of the Sun. One hundred and seventy-six starsexhibit Hα emission, and 82 stars have plausible X-raycounterparts from ROSAT observations. The distribution of chromosphericand coronal activity is broadly consistent with data for other nearbylate-type stars, with ~30 stars having activity levels comparable toPleiades M dwarfs. We have identified several M dwarfs that are probablywide ( >1000 AU) companions of F and G stars. We have recomputed the20 pc luminosity function, adding the 123 new candidates found in thepresent survey. The revised luminosity function is in closer agreementwith the 8 pc data set for stars with MJ>8 but probablyremains incomplete at the ~20% level.
| Proper Motions of the Jets in the Region of HH 30 and HL/XZ Tau: Evidence for a Binary Exciting Source of the HH 30 Jet
We present [S II] images of the HH 30 and HL/XZ Tau region obtained attwo epochs, as well as long-slit optical spectroscopy of the HH 30 jet.We measured proper motions of ~100-300 km s-1 for the HH 30jet and counterjet and of ~120 km s-1 for the HL Tau jet.Inclination angles with respect to the plane of the sky are0°-40° for the HH 30 jet and 60° for the HL Tau jet.Comparison with previous observations suggests that most of the jetknots consist of persistent structures. Also, we corroborate that the HH30-N knots correspond to the head of the HH 30 jet. The overall HH 30jet structure can be well described by a wiggling ballistic jet, arisingeither from orbital motion of the jet source around a primary or fromprecession of the jet axis because of the tidal effects of a companion.In the first scenario, the orbital period would be 53 yr and the totalmass 0.25-2 Msolar. In the precession scenario, the mass ofthe jet source would be ~0.1-1 Msolar, the orbital period<1 yr, and the mass of the companion less than a few times 0.01Msolar, thus being a substellar object or a giant exoplanet.In both scenarios a binary system with a separation <18 AU(<0.13") is required. Since the radius of the flared disk observedwith the HST is ~250 AU, we conclude that this disk appears to becircumbinary rather than circumstellar, suggesting that the search forthe collimating agent of the HH 30 jet should be carried out at muchsmaller scales.
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Osservazione e dati astrometrici
| Costellazione: | Microscopio |
| Ascensione retta: | 20h57m56.69s |
| Declinazione: | -33°38'56.9" |
| Magnitudine apparente: | 8.978 |
| Moto proprio RA: | 59.4 |
| Moto proprio Dec: | -78.1 |
| B-T magnitude: | 9.72 |
| V-T magnitude: | 9.04 |
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