Todd J. Henry

COOL SUBDWARF INVESTIGATIONS. I. NEW THOUGHTS ON THE SPECTRAL TYPES OF K AND M SUBDWARFS

Using new spectra of 88 K- and M-type subdwarfs, we consider novel methods for assigning their spectral types and take steps toward developing a comprehensive spectral sequence for subdwarf types K3.0 to M6.0. The types are assigned based on the overall morphology of spectra covering 6000-9000 A. The types and sequence presented link the spectral types of cool subdwarfs to their main-sequence counterparts, with emphasis on the relatively opacity-free region from 8200-9000 A. When available, supporting abundance, kinematic, and trigonometric parallax information is used to provide more complete portraits of the observed subdwarfs. We find that the CaHn (n = 1-3) and TiO5 indices often used for subdwarf spectral typing are affected in complicated ways by combinations of the subdwarfs temperatures, metallicities, and gravities, and we use model grids to evaluate the trends in all three parameters. Because of the complex interplay of these three characteristics, it is not possible to identify a star as an extreme subdwarf simply based on very low metallicity, and we suggest that the modifiers extreme or ultra only outline locations on spectroscopic indices plots, and should not be used to imply low or very low metallicity stars. In addition, we propose that VI be used to identify a star as a subdwarf, rather than the confusing sd prefix, which is also used for hot O and B subdwarfs that are unrelated to the cool subdwarfs discussed in this paper.

Two-color speckle imaging of M-dwarfs with the Discovery Channel telescope

Lowell Observatory and Southern Connecticut State University are currently involved in a joint project to determine the stellar multiplicity rates and the fundamental stellar parameters of M dwarf stars using the Differential Speckle Survey Instrument (DSSI) at Lowell’s Discovery Channel Telescope (DCT). DSSI observes speckle patterns simultaneously at two separate wavelengths, allowing color measurements of the components of a binary system to be made in a single observation. This paper will describe the initial data gathering process, which began in 2016. Since then, over 1000 stars have been observed. We summarize the analysis on these objects so far, and discuss the relevance of these observations for existing and future space missions such as TESS, JWST, and Gaia.

UCAC3 Proper Motion Survey. II. Discovery of New Proper Motion Stars in UCAC3 with 0farcs40 yr

We present 474 new proper motion stellar systems in the southern sky having no previously known components, with 0.40 yr{sup -1} >{mu} {>=} 0.18 yr{sup -1} between declinations -47 Degree-Sign and 0 Degree-Sign . In this second paper utilizing the U.S. Naval Observatory third CCD Astrograph Catalog (UCAC3) we complete our sweep of the southern sky for objects in the proper motion range targeted by this survey with R magnitudes ranging from 9.80 to 19.61. The new systems contribute a {approx}16% increase in the number of new stellar systems for the same region of sky reported in previous SuperCOSMOS Research Consortium On Nearby Stars (RECONS) surveys. Among the newly discovered stellar systems are 16 multiples, plus an additional ten components that are new common proper motion companions to previously known objects. A comparison of UCAC3 proper motions to those from Hipparcos, Tycho-2, Southern Proper Motion, and SuperCOSMOS indicates that all proper motions are consistent to {approx}10 mas yr{sup -1}, with the exception of SuperCOSMOS. Distance estimates are derived for all stellar systems having SuperCOSMOS Sky Survey B{sub J} , R{sub 59F}, and I{sub IVN} plate magnitudes and Two Micron All Sky Survey (2MASS) infrared photometry. We find five new redmorexa0» dwarf systems estimated to be within 25 pc. These discoveries support results from previous proper motion surveys suggesting that more nearby stellar systems are to be found, particularly in the fainter, slower moving samples. In this second paper utilizing the UCAC3 we complete our sweep of the southern sky for objects in the proper motion range targeted by this survey with R magnitudes ranging from 9.80 to 19.61.«xa0less

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We present 2817 new southern proper motion systems with 0.40 /yr > mu > 0.18 /yr and declination between -47 degrees and 00 degrees. This is a continuation of the SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky. We use the same photometric relations as previous searches to provide distance estimates based on the assumption that the objects are single main sequence stars. We find 79 new red dwarf systems predicted to be within 25 pc, including a few new components of previously known systems. Two systems - SCR 1731-2452 at 9.5 pc and SCR 1746-3214 at 9.9 pc - are anticipated to be within 10 pc. We also find 23 new white dwarf candidates with distance estimates of 15-66 pc, as well as 360 new red subdwarf candidates. With this search, we complete the SCR sweep of the southern sky for stars with mu > 0.18 /yr and R_59F < 16.5, resulting in a total of 5042 objects in 4724 previously unreported proper motion systems. Here we provide selected comprehensive lists from our SCR proper motion search to date, including 152 red dwarf systems estimated to be within 25 pc (nine within 10 pc), 46 white dwarfs (ten within 25 pc), and 598 subdwarf candidates. The results of this search suggest that there are more nearby systems to be found at fainter magnitudes and lower proper motion limits than those probed so far.