High Angular Resolution JHK Imaging of the Centers of the Metal-Poor Globular Clusters NGC5272 (M3), NGC6205 (M13), NGC6287, and NGC6341 (M92)

The Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) has been used to obtain high angular resolution JHK images of the centers of the metal-poor globular clusters NGC5272 (M3), NGC6205 (M13), NGC6287, and NGC6341 (M92). The color-magnitude diagrams (CMDs) derived from these data include the upper main sequence and most of the red giant branch (RGB), and the cluster sequences agree with published photometric measurements of bright stars in these clusters. The photometric accuracy is limited by PSF variations, which introduce systematic errors of a few hundredths of a magnitude near the AO reference star. The clusters are paired according to metallicity, and the near-infrared CMDs and luminosity functions are used to investigate the relative ages within each pair. The near-infrared CMDs provide the tightest constraints on the relative ages of the classical second parameter pair NGC5272 and NGC6205, and indicate that these clusters have ages that differ by no more than +/- 1 Gyr. These results thus support the notion that age is not the second parameter. We tentatively conclude that NGC6287 and NGC6341 have ages that differ by no more than +/- 2 Gyr. However, the near-infrared spectral energy distributions of stars in NGC6287 appear to differ from those of stars in outer halo clusters, bringing into question the validity of this age estimate.Comment: 22 pages, 17 figures. To be published in the Astronomical Journa

The Recent Stellar Archeology of M31 - The Nearest Red Disk Galaxy

We examine the star-forming history (SFH) of the M31 disk during the past few hundred Myr. The luminosity functions (LFs) of main sequence stars at distances R_GC > 21 kpc (i.e. > 4 disk scale lengths) are matched by models that assume a constant star formation rate (SFR). However, at smaller R_GC the LFs suggest that during the past ~10 Myr the SFR was 2 - 3 times higher than during the preceding ~100 Myr. The rings of cool gas that harbor a significant fraction of the current star-forming activity are traced by stars with ages ~100 Myr, indicating that (1) these structures have ages of at least 100 Myr, and (2) stars in these structures do not follow the same relation between age and random velocity as their counterparts throughout the disks of other spiral galaxies, probably due to the inherently narrow orbital angular momentum distribution of the giant molecular clouds in these structures. The distribution of evolved red stars is not azimuthally symmetric, in the sense that their projected density along the north east segment of the major axis is roughly twice that on the opposite side of the galaxy. The north east arm of the major axis thus appears to be a fossil star-forming area that dates to intermediate epochs. Such a structure may be the consequence of interactions with a companion galaxy.Comment: To appear in The Astrophysical Journa

Haffner 16: A Young Moving Group in the Making

The photometric properties of main sequence (MS) and pre-main sequence (PMS) stars in the young cluster Haffner 16 are examined using images recorded with the Gemini South Adaptive Optics Imager (GSAOI) and corrected for atmospheric blurring by the Gemini Multi-Conjugate Adapative Optics System (GeMS). A rich population of PMS stars is identified, and comparisons with isochrones suggest an age < 10 Myr assuming a distance modulus of 13.5 (D = 5 kpc). When compared with the solar neighborhood, Haffner 16 is roughly a factor of two deficient in objects with sub-solar masses. PMS objects in the cluster are also more uniformly distributed on the sky than bright MS stars. It is suggested that Haffner 16 is dynamically evolved, and that it is shedding protostars with sub-solar masses. Young low mass clusters like Haffner 16 are one possible source of PMS stars in the field. The cluster will probably evolve on time scales of ~ 100 - 1000 Myr into a diffuse moving group with a mass function that is very different from that which prevailed early in its life.Comment: To appear in the Publications of the Astronomical Society of the Pacifi

The Upper Asymptotic Giant Branch of the Elliptical Galaxy Maffei 1, and Comparisons with M32 and NGC 5128

Deep near-infrared images obtained with adaptive optics systems on the Gemini North and Canada-France-Hawaii telescopes are used to investigate the bright stellar content and central regions of the nearby elliptical galaxy Maffei 1. Stars evolving on the upper asymptotic giant branch (AGB) are resolved in a field 3 arcmin from the center of the galaxy. The locus of bright giants on the (K, H-K) color-magnitude diagram is consistent with a population of stars like those in Baade's Window reddened by E(H-K) = 0.28 +/- 0.05 mag. This corresponds to A_V = 4.5 +/- 0.8 mag, and is consistent with previous estimates of the line of sight extinction computed from the integrated properties of Maffei 1. The AGB-tip occurs at K = 20.0, which correponds to M_K = -8.7; hence, the AGB-tip brightness in Maffei 1 is comparable to that in M32, NGC 5128, and the bulges of M31 and the Milky-Way. The near-infrared luminosity functions (LFs) of bright AGB stars in Maffei 1, M32, and NGC 5128 are also in excellent agreement, both in terms of overall shape and the relative density of infrared-bright stars with respect to the fainter stars that dominate the light at visible and red wavelengths. It is concluded that the brightest AGB stars in Maffei 1, NGC 5128, M32, and the bulge of M31 trace an old, metal-rich population, rather than an intermediate age population. It is also demonstrated that Maffei 1 contains a distinct red nucleus, and this is likely the optical signature of low-level nuclear activity and/or a distinct central stellar population. Finally, there is an absence of globular clusters brighter than the peak of the globular cluster LF in the central 700 x 700 parsecs of Maffei 1.Comment: 22 pages of text and 9 postscript figures; to appear in the Astronomical Journa

Near-Infrared Adaptive Optics Imaging of the Central Regions of Nearby Sc Galaxies: I. M33

Near-infrared images obtained with the Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) are used to investigate the stellar content within 18 arcsec of the center of the Local Group spiral galaxy M33. AGB stars with near-infrared spectral-energy distributions similar to those of giants in the solar neighborhood and Baade's Window are detected over most of the field. The bolometric luminosity function (LF) of these stars has a discontinuity near M_{bol} = -5.25, and comparisons with evolutionary tracks suggest that most of the AGB stars formed in a burst of star formation 1 - 3 Gyr in the past. The images are also used to investigate the integrated near-infrared photometric properties of the nucleus and the central light concentration. The nucleus is bluer than the central light concentration, in agreement with previous studies at visible wavelengths. The CO index of the central light concentration 0.5 arcsec from the galaxy center is 0.05, which corresponds to [Fe/H] = -1.2 for simple stellar systems. Hence, the central light concentration could not have formed from the chemically-enriched material that dominates the present-day inner disk of M33.Comment: 23 pages of text + 11 figures; to appear in A

The Recent Star Formation History of NGC 5102

We present Hubble Space Telescope photometry of young stars in NGC 5102, a nearby gas-rich post-starburst S0 galaxy with a bright young stellar nucleus. We use the IAC-pop/MinnIAC algorithm to derive the recent star formation history in three fields in the bulge and disk of NGC 5102. In the disk fields, the recent star formation rate has declined monotonically and is now barely detectable, but a starburst is still in progress in the bulge and has added about 2 percent to the mass of the bulge over the last 200 Myr. Other studies of star formation in NGC 5102 indicate that about 20 percent of its stellar mass was added over the past Gyr. If this is correct, then much of the stellar mass of the bulge may have formed over this period. It seems likely that this star formation was fueled by the accretion of a gas-rich system with HI mass of about 2 x 10^9 Msol which has now been almost completely converted into stars. The large mass of recently formed stars and the blue colours of the bulge suggest that the current starburst, which is now fading, may have made a significant contribution to build the bulge of NGC 5102.Comment: 36 pages, 16 figures, accepted in A

Comparison of Single Leg Squat Variations on Lower Limb Muscle Activation and Center of Pressure Alterations

International Journal of Exercise Science 12(1): 950-959, 2019. Following anterior cruciate ligament reconstruction, individuals experience inadequate functioning of the quadriceps and decreased muscular strength. Decreased function delays return to physical activity and increases potential for re-injury. While several squat variations exist, a new variation has emerged in rehabilitation. The purpose of this study was to compare muscle activation of the Vastus Lateralis (VL), Vastus Medialis (VM), Rectus Femoris (RF), Gluteus Maximus (GM), and anterior posterior center of pressure (AP displacement) alterations during a single leg squat variation (SLS variation) versus a traditional split squat using electromyography (EMG) in healthy active females. Seventeen females performed one set of both squat variations on a force plate while muscle activation was measured. Paired t-tests were used to compare dependent variable (DV) means between squat variations. Results indicated SLS variation yielded lower peak and mean quadriceps activation compared to traditional split squat, (p \u3c 0.05). However, peak and mean GM muscle activity was greater in the SLS variation compared to the traditional split squat, (p \u3c 0.01). Lastly, AP displacement was greater during the SLS variation, (p \u3c 0.001). All three quadricep muscles had greater peak and mean EMG suggesting the traditional split squat be used for quadricep activation in rehabilitation/training settings, while the SLS variation should be prescribed for greater GM muscle activation. Understanding muscle activation patterns amongst squat variations can be practically applied by therapists, coaches and trainers to aid in reducing risks of arthrokinetic dysfunction via synergistic dominance, faster return to physical activity and normal functions of daily activity

The Evolved Red Stellar Contents of the Sculptor Group Galaxies NGC55, NGC300, and NGC7793

Deep J, H, and K images are used to probe the evolved stellar contents in the central regions of the Sculptor group galaxies NGC55, NGC300, and NGC7793. The brightest stars are massive red supergiants (RSGs) with K ~ 15 - 15.5. The peak RSG brightness is constant to within ~0.5 mag in K, suggesting that NGC55, NGC300, and NGC7793 are at comparable distances. Comparisons with bright RSGs in the Magellanic Clouds indicate that the difference in distance modulus with respect to the LMC is = 7.5. A rich population of asymptotic giant branch (AGB) stars, which isochrones indicate have ages between 0.1 and 10 Gyr, dominates the (K, J-K) color-magnitude diagram (CMD) of each galaxy. The detection of significant numbers of AGB stars with ages near 10 Gyr indicates that the disks of these galaxies contain an underlying old population. The CMDs and luminosity functions reveal significant galaxy-to-galaxy variations in stellar content. Star-forming activity in the central arcmin of NGC300 has been suppressed for the past Gyr with respect to disk fields at larger radii. Nevertheless, comparisons between fields within each galaxy indicate that star-forming activity during intermediate epochs was coherent on spatial scales of a kpc or more. A large cluster of stars, which isochrones suggest has an age near 100 Myr, is seen in one of the NGC55 fields. The luminosity function of the brightest stars in this cluster is flat, as expected if a linear luminosity-core mass relation is present.Comment: 30 pages, including 13 figure

The Neutral Hydrogen Bridge between M31 and M33

The Green Bank Telescope has been used to search for 21cm HI emission over a large area between the galaxies M31 and M33 in an attempt to confirm at 9.1 arcmin angular resolution the detection by Braun and Thilker (2004) of a very extensive neutral gas "bridge" between the two systems at the level NHI approximately 10^{17} cm^{-2}. We detect HI emission at several locations up to 120 kpc in projected distance from M31, at least half the distance to M33, with velocities similar to that of the galaxies, confirming the essence of the Braun and Thilker discovery. The HI does not appear to be associated with the extraplanar high-velocity clouds of either galaxy. In two places we measure NHI > 3 x 10^{18} cm^{-2}, indicative of concentrations of HI with ~10^5 solar masses on scales <2 kpc, but over most of the field we have only 5sigma upper limits of NHI <= 1.4 x 10^{18} cm^{-2}. In very deep measurements in two directions HI lines were detected at a few 10^{17} cm^{-2}. The absence of emission at another location to a 5sigma limit NHI <= 1.5 x 10^{17} cm^{-2} suggests that the HI bridge is either patchy or confined to within ~125 kpc of M31. The measurements also cover two of M31's dwarf galaxies, And II and And XV, but in neither case is there evidence for associated HI at the 5sigma level of 1.4 x 10^4 solar masses of HI for And II, and 9.3 x 10^3 solar masses for And XV.Comment: Submitted to the Astronomical Journa