Browsing by Subject "lower main-sequence"
Now showing 1 - 4 of 4
- Results Per Page
- Sort Options
Item The ACS Survey Of Galactic Globular Clusters. VI. NGC 6366: A Heavily Stripped Galactic Globular Cluster(2009-01) Paust, Nathaniel E. Q.; Aparicio, Antonio; Piotto, Giampaolo; Reid, I. Neill; Anderson, Jay; Sarajedini, Ata; Bedin, Luigi R.; Chaboyer, Brian; Dotter, Aaron; Hempel, Maren; Majewski, Steven; Marin-Franch, A.; Milone, Antonio; Rosenberg, Alfred; Siegel, Michael; Siegel, MichaelWe have used observations obtained as part of the Hubble Space Telescope/ACS Survey of Galactic globular clusters (GCs) to construct a color-magnitude diagram for the bulge cluster, NGC 6366. The luminosity function derived from those data extends to M(F606W) similar to 9, or masses of similar to 0.3 M(circle dot). Unlike most GCs, the mass function peaks near the main-sequence turnoff with significantly fewer low-mass stars even after correction for completeness and mass segregation. Using a multimass King model, we extrapolate the global cluster behavior and find the global mass function to be poorly matched by a power law, with a particular deficit of stars with masses between 0.5 and 0.7 M(circle dot). We briefly discuss this interesting anomaly within the context of tidal stripping.Item The ACS Survey Of Galactic Globular Clusters. VIII. Effects Of Environment On Globular Cluster Global Mass Functions(2010-02) Paust, Nathaniel EQ; Reid, I. Neill; Piotto, Giampaolo; Aparicio, Antonio; Anderson, Jay; Sarajedini, Ata; Bedin, Luigi R.; Chaboyer, Brian; Dotter, Aaron; Hempel, Maren; Majewski, Steven; Marin-Franch, A.; Milone, Antonio; Rosenberg, Alfred; Siegel, Michael; Siegel, MichaelWe have used observations obtained as part of the Hubble Space Telescope/ACS Survey of Galactic Globular Clusters to construct global present-day mass functions for 17 globular clusters utilizing multi-mass King models to extrapolate from our observations to the global cluster behavior. The global present-day mass functions for these clusters are well matched by power laws from the turnoff, approximate to 0.8 M(circle dot), to 0.2-0.3 M(circle dot) on the lower main sequence. The slopes of those power-law fits, alpha, have been correlated with an extensive set of intrinsic and extrinsic cluster properties to investigate which parameters may influence the form of the present-day mass function. We do not confirm previous suggestions of correlations between alpha and either metallicity or Galactic location. However, we do find a strong statistical correlation with the related parameters central surface brightness, mu(V), and inferred central density, rho(0). The correlation is such that clusters with denser cores (stronger binding energy) tend to have steeper mass functions (a higher proportion of low-mass stars), suggesting that dynamical evolution due to external interactions may have played a key role in determining alpha. Thus, the present-day mass function may owe more to nurture than to nature. Detailed modeling of external dynamical effects is therefore a requisite for determining the initial mass function for Galactic globular clusters.Item The Factory And The Beehive. II. Activity And Rotation In Praesepe And The Hyades(2014-11) Douglas, S. T.; Agueros, M. A.; Covey, Kevin R.; Bowsher, E. C.; Bochanski, J. J.; Cargile, P. A.; Kraus, Adam; Law, N. M.; Lemonias, J. J.; Arce, Hector G.; Fierroz, D. F.; Kundert, A.; Kraus, AdamOpen clusters are collections of stars with a single, well-determined age, and can be used to investigate the connections between angular-momentum evolution and magnetic activity over a star's lifetime. We present the results of a comparative study of the relationship between stellar rotation and activity in two benchmark open clusters: Praesepe and the Hyades. As they have the same age and roughly solar metallicity, these clusters serve as an ideal laboratory for testing the agreement between theoretical and empirical rotation-activity relations at approximate to 600 Myr. We have compiled a sample of 720 spectra-more than half of which are new observations-for 516 high-confidence members of Praesepe; we have also obtained 139 new spectra for 130 high-confidence Hyads. We have also collected rotation periods (P-rot) for 135 Praesepe members and 87 Hyads. To compare H alpha emission, an indicator of chromospheric activity, as a function of color, mass, and Rossby number R-o, we first calculate an expanded set of chi values, with which we can obtain the H alpha to bolometric luminosity ratio, L-H alpha/L-bol, even when spectra are not flux-calibrated and/or stars lack reliable distances. Our. values cover a broader range of stellar masses and colors (roughly equivalent to spectral types from K0 to M9), and exhibit better agreement between independent calculations, than existing values. Unlike previous authors, we find no difference between the two clusters in their H alpha equivalent width or L-H alpha/L-bol distributions, and therefore take the merged H alpha and Prot data to be representative of 600 Myr old stars. Our analysis shows that H alpha activity in these stars is saturated for R-o <= 0.11(-0.03)(+0.02) Above that value activity declines as a power-law with slope beta = -0.73(-0.12,)(+0.06) before dropping off rapidly at Ro approximate to 0.4. These data provide a useful anchor for calibrating the age-activity-rotation relation beyond 600 Myr.Item Spin-Orbit Alignment for the Circumbinary Planet Host Kepler-16 A(2011-11) Winn, Joshua N.; Albrecht, Simon; Johnson, John Asher; Torres, Guillermo; Cochran, William D.; Marcy, Geoffrey W.; Howard, Andrew W.; Isaacson, Howard; Fischer, Debra; Doyle, Laurance; Welsh, William; Carter, Joshua A.; Fabrycky, Daniel C.; Ragozzine, Darin; Quinn, Samuel N.; Shporer, Avi; Howell, Steve B.; Latham, David W.; Orosz, Jerome; Prsa, Andrej; Slawson, Robert W.; Borucki, William J.; Koch, David; Barclay, Thomas; Boss, Alan P.; Christensen-Dalsgaard, Jorgen; Girouard, Forrest R.; Jenkins, Jon; Klaus, Todd C.; Meibom, Soren; Morris, Robert L.; Sasselov, Dimitar; Still, Martin; Van Cleve, Jeffrey; Cochran, William D.Kepler-16 is an eccentric low-mass eclipsing binary with a circumbinary transiting planet. Here, we investigate the angular momentum of the primary star, based on Kepler photometry and Keck spectroscopy. The primary star's rotation period is 35.1 +/- 1.0 days, and its projected obliquity with respect to the stellar binary orbit is 1.degrees 6 +/- 2.degrees 4. Therefore, the three largest sources of angular momentum-the stellar orbit, the planetary orbit, and the primary's rotation-are all closely aligned. This finding supports a Formation scenario involving accretion from a single disk. Alternatively, tides may have realigned the stars despite their relatively wide separation (0.2 AU), a hypothesis that is supported by the agreement between the measured rotation period and the "pseudosynchronous" period of tidal evolution theory. The rotation period, chromospheric activity level, and fractional light variations suggest a main-sequence age of 2-4 Gyr. Evolutionary models of low-mass stars can match the observed masses and radii of the primary and secondary stars to within about 3%.