We present spectroscopic rotation velocities (v sin i) for 56 M dwarf stars using high-resolution Hobby-Eberly Telescope High Resolution Spectrograph red spectroscopy. In addition, we have also determined photometric effective temperatures, masses, and metallicities ([Fe/H]) for some stars observed here and in the literature where we could acquire accurate parallax measurements and relevant photometry. We have increased the number of known v sin i values for mid M stars by around 80% and can confirm a weakly increasing rotation velocity with decreasing effective temperature. Our sample of v sin is peak at low velocities (∼3 km s −1 ). We find a change in the rotational velocity distribution between early M and late M stars, which is likely due to the changing field topology between partially and fully convective stars. There is also a possible further change in the rotational distribution toward the late M dwarfs where dust begins to play a role in the stellar atmospheres. We also link v sin i to age and show how it can be used to provide mid-M star age limits. When all literature velocities for M dwarfs are added to our sample, there are 198 with v sin i 10 km s −1 and 124 in the mid-to-late M star regime (M3.0-M9.5) where measuring precision optical radial velocities is difficult. In addition, we also search the spectra for any significant Hα emission or absorption. Forty three percent were found to exhibit such emission and could represent young, active objects with high levels of radial-velocity noise. We acquired two epochs of spectra for the star GJ1253 spread by almost one month and the Hα profile changed from showing no clear signs of emission, to exhibiting a clear emission peak. Four stars in our sample appear to be low-mass binaries (GJ1080, GJ3129, Gl802, and LHS3080), with both GJ3129 and Gl802 exhibiting double Hα emission features. The tables presented here will aid any future M star planet search target selection to extract stars with low v sin i.

Aims. We present the results from high-resolution spectroscopic measurements to determine metallicities and activities of bright stars in the southern hemisphere. Methods. We measured the iron abundances ([Fe/H]'s) and chromospheric emission indices (log hR HK ) of 353 solar-type stars with V = 7.5−9.5. [Fe/H] abundances are determined using a custom χ 2 fitting procedure within a large grid of Kurucz model atmospheres. The chromospheric activities were determined by measuring the amount of emission in the cores of the strong Caii HK lines. Results. Our comparison of the metallicity sample to other [Fe/H] determinations was found to agree at the ±0.05 dex level for spectroscopic values and at the ±0.1 dex level for photometric values. The distribution of chromospheric activities is described by a bimodal distribution, agreeing with the conclusions from other works. Also an analysis of Maunder minimum status was attempted, and it was found that 6 ± 4 stars in the sample could be in a Maunder minimum phase of their evolution and hence the Sun should only spend a few per cent of its main sequence lifetime in Maunder minimum.

We build an accurate data base of 5200 HCN and HNC rotation–vibration energy levels, determined from existing laboratory data. 20 000 energy levels in the Harris et al. linelist are assigned approximate quantum numbers. These assignments, lab‐determined energy levels and Harris et al. energy levels are incorporated in to a new energy level list. A new linelist is presented, in which frequencies are computed using the lab‐determined energy levels where available, and the ab initio energy levels otherwise. The new linelist is then used to compute new model atmospheres and synthetic spectra for the carbon star WZ Cas. This results in better fit to the spectrum of WZ Cas in which the absorption feature at 3.56 μm is reproduced to a higher degree of accuracy than has previously been possible. We improve the reproduction of HCN absorption features by reducing the abundance of Si to [Si/H]=−0.5 dex, however, the strengths of the Δv= 2 CS band heads are overpredicted.

Determination of the lithium depletion boundary (LDB), i.e., the observational limit below which the cores of very low-mass objects do not reach high enough temperature for Li destruction, has been used to obtain ages for several open clusters and stellar associations younger than 200 Myr, which until now has been considered as the practical upper limit on the range of applicability of this method. In this work we show that the LDB method can be extended to significant older ages than previously thought. Intermediate resolution optical spectra of six L-type candidate members in the Hyades cluster obtained using OSIRIS at the 10.4-m Gran Telescopio Canarias are presented. The Li I 670.8 nm resonance doublet is clearly detected only in the two faintest and coolest of these objects, which are classified as L3.5 to L4 brown dwarf cluster members with luminosities around 10 −4 solar. Lithium depletion factors are estimated for our targets with the aid of synthetic spectra and they are compared with predictions from evolutionary models. A LDB age of 650±70 Myr for the Hyades provides a consistent description of our data using a set of state-of-the-art evolutionary models for brown dwarfs calculated by Baraffe et al. (2015).

We measured lithium in a sample of low-mass stars (∼0.1-0.3 ) of the Orion Nebula cluster. We find M , evidence for significant Li depletion in four high-probability members, corresponding to nuclear ages between ∼15 and 30 Myr. In two cases, there is excellent agreement between the mass and age based on models of Li burning and those derived from the H-R diagram, reinforcing our early findings. For the two other stars, the nuclear age is significantly larger than the isochronal one. Several Li-depleted stars display accretion activity, veiling, and emission lines. We discuss empirical evidence in favor of the old nuclear age and the implications on the star formation history of the Orion cluster.

No abstract

Since M4.5 -M9 dwarfs exhibit equatorial rotation velocities of order 10 kms −1 on average, radial velocity surveys targeting this stellar population will likely need to find methods to effectively remove starspot jitter. We present the first high resolution Doppler images of the M4.5 dwarf, GJ 791.2A, and the M9 dwarf, LP 944-20. The time series spectra of both objects reveal numerous line profile distortions over the rotation period of each star which we interpret as starspots. The transient distortions are modelled with spot/photosphere contrast ratios that correspond to model atmosphere temperature differences of T phot -T spot = 300 K and 200 K. GJ 791.2A is a fully convective star with v sin i = 35.1 kms −1 . Although we find more starspot structure at high latitudes, we reconstruct spots at a range of phases and latitudes with a mean spot filling of ∼ 3%. LP 944-20 is one of the brightest known late-M dwarfs, with spectral type M9V and v sin i = 30.8 kms −1 . Its spectral time series exhibits two dominant transient line distortions that are reconstructed as high latitude spots, while a mean spot filling factor of only 1.5% is found. The occurrence of low-contrast spots at predominantly high latitudes, which we see in both targets here, is in general likely to be responsible for the low amplitude photometric variability seen in late-M dwarfs. For GJ 791.2A, the radial velocities induced by the starspot features yield an r.m.s. velocity variability of 138 ms −1 , which can be reduced by a factor of 1.9 using our reconstructed surface brightness distributions.

We present eight new T4.5–T7.5 dwarfs identified in the UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) Data Release 1 (DR1). In addition we have recovered the T4.5 dwarf SDSS J020742.91+000056.2 and the T8.5 dwarf ULAS J003402.77−005206.7. Photometric candidates were picked up in two‐colour diagrams over 190 deg2 (DR1) and selected in at least two filters. All candidates exhibit near‐infrared spectra with strong methane and water absorption bands characteristic of T dwarfs and the derived spectral types follow the unified scheme of Burgasser et al.. We have found six new T4.5–T5.5 dwarfs, one T7 dwarf, one T7.5 dwarf and recovered a T4.5 dwarf and a T8.5 dwarf. We provide distance estimates which lie in the 15–85 pc range; the T7.5 and T8.5 dwarfs are probably within 25 pc of the Sun. We conclude with a discussion of the number of T dwarfs expected after completion of the LAS, comparing these initial results to theoretical simulations.