The Isaac Newton Telescope (INT) Photometric H‐Alpha Survey (IPHAS) is a 1800 deg2 survey of the Northern Galactic Plane, reaching down to r′∼ 21. We demonstrate how the survey can be used to (1) reliably select classical T Tauri star candidates and (2) constrain the mass accretion rates with an estimated relative uncertainty of 0.6 dex. IPHAS is a necessary addition to spectroscopic surveys because it allows large and uniform samples of accretion rates to be obtained with a precise handle on the selection effects. We apply the method on a region of 7 deg2 towards the H ii region IC 1396 in Cepheus OB2 and identify 158 pre‐main‐sequence candidates with masses between 0.2 and 2.0 M⊙ and accretion rates between 10−9.2 and 10−7.0 M⊙ yr−1. We find a power‐law dependency between the stellar mass and the accretion rates with a slope of α= 1.1 ± 0.2, which is less steep than indicated by previous studies. We discuss the influence of method‐dependent systematic effects on the determination of this relationship. The majority of our sample consists of faint, previously unknown, low‐mass T Tauri candidates (56 per cent between 0.2 and 0.5 M⊙). Many candidates are clustered in front of three bright‐rimmed molecular clouds, which are being ionized by the massive star HD 206267 (O6.5V). We discover a spatio‐temporal gradient of increasing accretion rates, increasing Spitzer infrared excess, and younger ages away from the ionizing star, providing a strong indication that the formation of these clusters has been sequentially triggered by HD 206267 during the last ∼1 Myr.

Recent studies of the substellar population in the Taurus cloud have revealed a deficit of brown dwarfs compared to the Trapezium cluster population. However, these works have concentrated on the highest stellar density regions of the Taurus cloud. We have performed a large scale optical survey of this region, covering a total area of 28 deg 2 , and encompassing the densest parts of the cloud as well as their surroundings, down to a mass detection limit of 15 M J . We present the optical spectroscopic follow-up observations of 97 photometrically selected potential new low-mass Taurus members, of which 27 are strong late-M spectral type (SpT ≥ M4V) candidates. Our spectroscopic survey is 87% complete down to i = 20 for spectral types later than M4V, which corresponds to a mass completeness limit of 30 M J for ages ≤10 Myr and Av ≤ 4. We derive spectral types, visual absorption and luminosity class estimates and discuss our criteria to assess Taurus membership. These observations reveal 5 new VLM Taurus members and 12 new BDs. Two of the new VLM sources and four of the new substellar members exhibit accretion/outflow signatures similar to higher mass classical T Tauri stars. From levels of Hα emission we derive a fraction of accreting sources of 42% in the substellar Taurus population. Combining our observations with previously published results, we derive an updated substellar to stellar ratio in Taurus of R ss = 0.23 ± 0.05. This ratio now appears consistent with the value previously derived in the Trapezium cluster under similar assumptions of 0.26 ± 0.04. We find indications that the relative numbers of BDs with respect to stars is decreased by a factor 2 in the central regions of the aggregates with respect to the more distributed population. Our findings are best explained in the context of the embryo-ejection model where brown dwarfs originate from dynamical interactions in small N unstable multiple systems.

We present 10 m Keck spectra of the two Pleiades brown dwarfs Teide 1 and Calar 3 showing a clear detection of the 670.8 nm Li resonance line. In Teide 1, we have also obtained evidence for the presence of the subordinate line at 812.6 nm. A high Li abundance (log N(Li) >= 2.5), consistent with little if any depletion, is inferred from the observed lines. Since Pleiades brown dwarfs are unable to burn Li the significant preservation of this fragile element confirms the substellar nature of our two objects. Regardless of their age, their low luminosities and Li content place Teide 1 and Calar 3 comfortably in the genuine brown dwarf realm. Given the probable age of the Pleiades cluster, their masses are estimated at 55 +- 15 Jupiter masses.Comment: 14 pages gzipped and uuencoded. Figures are included. Also available at http://www.iac.es/. Accepted for publication in ApJ Letter

We have identified four brown dwarfs in the Taurus star-forming region. They were first selected from R and I CCD photometry of 2.29 square degrees obtained at the Canada-France-Hawaii Telescope. Subsequently, they were recovered in the 2MASS second incremental data release point source catalog. Low-resolution optical spectra obtained at the William Herschel telescope allow us to derive spectral types in the range M7-M9. One of the brown dwarfs has very strong Hα emission (EW=-340 Å ). It also displays Brγ emission in an infrared spectrum obtained with IRCS on the Subaru telescope, suggesting that it is accreting matter from a disk. The K I resonance doublet and the Na I subordinate doublet at 818.3 and 819.5 nm in these Taurus objects are weaker than in field dwarfs of similar spectral type, consistent with low surface gravities as expected for young brown dwarfs. Two of the objects are cooler and fainter than GG Tau Bb, the lowest mass known member of the Taurus association. We estimate masses of only 0.03 M ⊙ for them. The spatial distribution of brown dwarfs in Taurus hints to a possible anticorrelation between the density of stars and the density of brown dwarfs.

We have obtained radial velocities of a sample of 18 ultracool dwarfs (M6.5YT8) using high-resolution, nearinfrared spectra obtained with NIRSPEC and the Keck II telescope. We have confirmed that the radial velocity of Gl 570D is coincident with that of the K-type primary star Gl 570A, thus providing additional support for their true companionship. The presence of planetary-mass companions around 2MASS J05591914À1404488 (T4.5 V ) has been analyzed using five NIRSPEC radial velocity measurements obtained over a period of 4.37 yr. We have computed UVW space motions for a total of 21 L and T dwarfs within 20 pc of the Sun. This population shows UVW velocities that nicely overlap the typical kinematics of solar to M-type stars within the same spatial volume. However, the mean Galactic and tangential velocities of the L and T dwarfs appear to be smaller than those of G to M stars. A significant fraction ($40%) of the ultracool dwarfs lie near the Hyades moving group (0.4Y2 Gyr), which contrasts with the 10%Y12% found for earlier type stellar neighbors. In addition, the distributions of the UVW components and the distributions of the total Galactic and tangential velocities derived for the L and T sample are narrower than those measured for nearby G-, K-, and M-type stars, but similar to the dispersions obtained for F stars. This suggests that, in the solar neighborhood, the population of L-and T-type ultracool dwarfs (including brown dwarfs) is kinematically younger than solar-type to early M stars, with likely ages in the interval 0.5Y4 Gyr.