5,742 research outputs found
Exploring Halo Substructure with Giant Stars: The Dynamics and Metallicity of the Dwarf Spheroidal in Bootes
We report the results of a spectroscopic study of the Bootes (Boo) dwarf
spheroidal (dSph) galaxy carried out with the WIYN telescope and the Hydra
multifiber spectrograph. Radial velocities have been measured for 58 Boo
candidate stars selected to have magnitudes and colors consistent with its red
and asymptotic giant branches. Within the 13' half-light radius, seven members
of Boo yield a systemic velocity of V_r=95.6+-3.4 km/s and a velocity
dispersion of 6.6+-2.3 km/s. This implies a mass on the order of 1 x 10^7
M_sun, similar to the inferred masses of other Galactic dSphs. Adopting a total
Boo luminosity of L=1.8 x 10^4 L_sun to 8.6 x 10^4 L_sun implies M/L ~ 610 to
130, making Boo, the most distorted known Milky Way dwarf galaxy, potentially
also the darkest. From the spectra of Boo member stars we estimate its
metallicity to be [Fe/H] ~ -2.5, which would make it the most metal poor dSph
known to date.Comment: Accepted for publication in ApJ Letter
The shapes of Milky Way satellites: looking for signatures of tidal stirring
We study the shapes of Milky Way satellites in the context of the tidal
stirring scenario for the formation of dwarf spheroidal galaxies. The standard
procedures used to measure shapes involve smoothing and binning of data and
thus may not be sufficient to detect structural properties like bars, which are
usually subtle in low surface brightness systems. Taking advantage of the fact
that in nearby dwarfs photometry of individual stars is available we introduce
discrete measures of shape based on the two-dimensional inertia tensor and the
Fourier bar mode. We apply these measures of shape first to a variety of
simulated dwarf galaxies formed via tidal stirring of disks embedded in dark
matter halos and orbiting the Milky Way. In addition to strong mass loss and
randomization of stellar orbits, the disks undergo morphological transformation
that typically involves the formation of a triaxial bar after the first
pericenter passage. These tidally induced bars persist for a few Gyr before
being shortened towards a more spherical shape if the tidal force is strong
enough. We test this prediction by measuring in a similar way the shape of
nearby dwarf galaxies, satellites of the Milky Way. We detect inner bars in
Ursa Minor, Sagittarius, LMC and possibly Carina. In addition, six out of
eleven studied dwarfs show elongated stellar distributions in the outer parts
that may signify transition to tidal tails. We thus find the shapes of Milky
Way satellites to be consistent with the predictions of the tidal stirring
model.Comment: 14 pages, 11 figures, accepted for publication in Ap
A Deep Proper-Motion Survey in Kapteyn Selected Areas: I. Survey Description and First Results for Stars in the Tidal Tail of Sagittarius and in the Monoceros Ring
We describe a high-precision, deep (to V ~ 19-21) absolute proper-motion
survey that samples ~50 lines of sight in the Kapteyn Selected Areas along
declination zones -15, 0 and 15 degrees. In many fields the astrometric
baseline reaches nearly a century. We demonstrate that these data provide
typical per star precisions between ~ 1 and 3 mas/yr to the above magnitude
limits, with the absolute reference frame established by numerous extragalactic
sources in each survey field. Combined with existing and ongoing photometric
and radial velocity surveys in these fields, these astrometric data will
enable, among other things, accurate, detailed dynamical modeling of satellite
interactions with our Galaxy. In this contribution we describe the astrometric
part of our survey and show preliminary results along the trailing tail of the
Sagittarius dwarf galaxy, and in the Monoceros ring region.Comment: Accepter for publication in the Astronomical Journa
Kinematics and Metallicities in the Boötes III Stellar Overdensity: A Disrupted Dwarf Galaxy?
We report the results of a spectroscopic study of the Boötes III (BooIII) stellar overdensity carried out with the Hectospec multifiber spectrograph on the MMT telescope. Radial velocities have been measured for 193 BooIII candidate stars selected to have magnitudes and colors consistent with its upper main sequence and lower red giant branch, as well as a number of horizontal-branch candidates. From 20 identified candidate BooIII members, we measure a systemic velocity of V_â = 197.5 ± 3.8 km s^(â1) and a velocity dispersion of Ï_o = 14.0 ± 3.2 km s^(â1). We use the somewhat large velocity dispersion and the implied highly radial orbit, along with morphological evidence from Grillmair and stellar abundances, to argue that BooIII is likely the first known object observed in a transitional state between being a bound dwarf galaxy and a completely unbound tidal stream
Effect of growth-promoting technologies on Longissimus lumborum muscle fiber morphometrics, collagen solubility, and cooked meat tenderness
Citation: Ebarb, S. M., Drouillard, J. S., Maddock-Carlin, K. R., Phelps, K. J., Vaughn, M. A., Burnett, D. D., . . . Gonzalez, J. M. (2016). Effect of growth-promoting technologies on Longissimus lumborum muscle fiber morphometrics, collagen solubility, and cooked meat tenderness. Journal of Animal Science, 94(2), 869-881. doi:10.2527/jas2015-9888The objective of the study was to examine the effect of growth-promoting technologies (GP) on Longissimus lumborum steak tenderness, muscle fiber cross-sectional area (CSA), and collagen solubility. Crossbred feedlot heifers (n = 33; initial BW 464 +/- 6 kg) were blocked by BW and assigned to 1 of 3 treatments: no GP (CON; n = 11); implant, no zilpaterol hydrochloride (IMP; n = 11); implant and zilpaterol hydrochloride (COMBO; n = 11). Heifers assigned to receive an implant were administered Component TE-200 on d 0 of the study, and the COMBO group received 8.3 mg/kg DM of zilpaterol hydrochloride for the final 21 d of feeding with a 3 d withdrawal period. Following harvest, strip loins were collected and fabricated into 4 roasts and aged for 3, 14, 21, or 35 d postmortem. Fiber type was determined by immunohistochemistry. After aging, objective tenderness and collagen solubility were measured. There was a treatment x day of aging (DOA) interaction for Warner-Bratzler shear force (WBSF; P 0.31). Soluble collagen amount tended to be affected (P = 0.06) by a treatment x DOA interaction which was due to COMBO muscle having more soluble collagen than the other 2 treatments on d 21 of aging (P < 0.02). Correlation analysis indicated that type I, IIA, and IIX fiber CSA are positively correlated with WBSF at d 3 and 14 of aging (P < 0.01), but only type IIX fibers are correlated at d 21 and 35 of aging (P < 0.03). At these time periods, total and insoluble collagen became positively correlated with WBSF (P < 0.01). This would indicate that relationship between muscle fiber CSA and WBSF decreases during postmortem aging, while the association between WBSF and collagen characteristics strengthens. The use of GP negatively impacted meat tenderness primarily through increased muscle fiber CSA and not through altering collagen solubility
Effects of anabolic implants and ractopamine-HCl on muscle fiber morphometrics, collagen solubility, and tenderness of beef longissimus lumborum steaks
Citation: Ebarb, S. M., Phelps, K. J., Drouillard, J. S., Maddock-Carlin, K. R., Vaughn, M. A., Burnett, D. D., . . . Gonzalez, J. M. (2017). Effects of anabolic implants and ractopamine-HCl on muscle fiber morphometrics, collagen solubility, and tenderness of beef longissimus lumborum steaks. Journal of Animal Science, 95(3), 1219-1231. doi:10.2527/jas2016.1263The objective of this study was to examine the effects of growth-promoting technologies (GP) and postmortem aging on longissimus lumborum muscle fiber cross-sectional area (CSA), collagen solubility, and their relationship to meat tenderness. Two groups of black-hided crossbred feedlot heifers (group 1: n = 33, initial BW 430 +/- 7 kg; group 2: n = 32, initial BW 466 +/- 7 kg) were blocked by BW and assigned to 1 of 3 treatments consisting of: no implant and no ractopamine hydrochloride (CON; n = 21); implant, no ractopamine hydrochloride (IMP; n = 22); implant and ractopamine hydrochloride (COMBO; n = 22). Heifers that received an implant were administered an implant containing 200 mg trenbolone acetate and 20 mg estradiol on d 0 of the study, and heifers in the COMBO group received 400 mg.head(-1).d(-1) of ractopamine hydrochloride for 28 (Group 1) or 29 d (Group 2) at the end of 90-(Group 1) or 106-d (Group 2) feeding period. Following harvest, strip loins were collected and further fabricated into 5 roasts for postmortem aging (DOA) periods of 2, 7, 14, 21, or 35 d. After aging, Warner-Bratzler shear force (WBSF), muscle fiber CSA, and collagen solubility were measured. There was no treatment x DOA interaction for WBSF (P = 0.86), but treatment and DOA impacted WBSF (P 0.33). Collagen amounts were not impacted by GP treatment (P > 0.72), but DOA increased the concentration of soluble collagen (P = 0.04). Fiber CSA of all fiber types were positively correlated (P < 0.05; r = 0.21 to 0.28) with WBSF only on d 2 of aging, while soluble collagen amount tended to negatively correlate with WBSF on d 7 and 14 of aging (P < 0.10; r = -0.24 and -0.23, respectively). Administration of GP during heifer finishing resulted in greater steak WBSF over 35 d of aging, which was not due to collagen characteristics and only minimally affected by fiber CSA
The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
We measure the Milky Way's rotation curve over the Galactocentric range 4 kpc
<~ R <~ 14 kpc from the first year of data from the Apache Point Observatory
Galactic Evolution Experiment (APOGEE). We model the line-of-sight velocities
of 3,365 stars in fourteen fields with b = 0 deg between 30 deg < l < 210 deg
out to distances of 10 kpc using an axisymmetric kinematical model that
includes a correction for the asymmetric drift of the warm tracer population
(\sigma_R ~ 35 km/s). We determine the local value of the circular velocity to
be V_c(R_0) = 218 +/- 6 km/s and find that the rotation curve is approximately
flat with a local derivative between -3.0 km/s/kpc and 0.4 km/s/kpc. We also
measure the Sun's position and velocity in the Galactocentric rest frame,
finding the distance to the Galactic center to be 8 kpc < R_0 < 9 kpc, radial
velocity V_{R,sun} = -10 +/- 1 km/s, and rotational velocity V_{\phi,sun} =
242^{+10}_{-3} km/s, in good agreement with local measurements of the Sun's
radial velocity and with the observed proper motion of Sgr A*. We investigate
various systematic uncertainties and find that these are limited to offsets at
the percent level, ~2 km/s in V_c. Marginalizing over all the systematics that
we consider, we find that V_c(R_0) 99% confidence. We find an
offset between the Sun's rotational velocity and the local circular velocity of
26 +/- 3 km/s, which is larger than the locally-measured solar motion of 12
km/s. This larger offset reconciles our value for V_c with recent claims that
V_c >~ 240 km/s. Combining our results with other data, we find that the Milky
Way's dark-halo mass within the virial radius is ~8x10^{11} M_sun.Comment: submitted to Ap
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