66 research outputs found
Star formation rates as a function of galaxy mass
Correlations were found between the colors and absolute magnitudes of spiral galaxies. Using optical and/or near IR (1.6 micron) colors, it was found that lower luminosity spirals are systematically bluer than higher luminosity spirals. Infrared Astronomy Satellite (IRAS) far IR luminosities were used to investigate the suggestion that one prime cause of these color-absolute magnitude correlations is a systematic variation with galaxy mass of the current star formation rate (SFR) per unit mass. To the extent that the IRAS fluxes actually measure disk SFR, no correlation of SFR/unit mass and galaxy mass was found. Other possible explanations of the color-absolute magnitude correlations are discussed, as well as caveats on the use of IRAS fluxes as a means of comparing SFRs in galaxies of differing mass
Colors of Inner Disk Classical Kuiper Belt Objects
We present new optical broadband colors, obtained with the Keck 1 and Vatican
Advanced Technology telescopes, for six objects in the inner classical Kuiper
Belt. Objects in the inner classical Kuiper Belt are of interest as they may
represent the surviving members of the primordial Kuiper Belt that formed
interior to the current position of the 3:2 resonance with Neptune, the current
position of the plutinos, or, alternatively, they may be objects formed at a
different heliocentric distance that were then moved to their present
locations. The six new colors, combined with four previously published, show
that the 10 inner belt objects with known colors form a neutral clump and a
reddish clump in B-R color. Nonparametric statistical tests show no significant
difference between the B-R color distribution of the inner disk objects
compared to the color distributions of Centaurs, plutinos, or scattered disk
objects. However, the B-R color distribution of the inner classical Kuiper belt
objects does differ significantly from the distribution of colors in the cold
(low inclination) main classical Kuiper belt. The cold main classical objects
are predominately red, while the inner classical belt objects are a mixture of
neutral and red. The color difference may reveal the existence of a gradient in
the composition and /or surface processing history in the primordial Kuiper
Belt, or indicate that the inner disk objects are not dynamically analogous to
the cold main classical belt objects.Comment: Accepted for publication in A
Statistical Connections Between the Properties of Type Ia Supernovae and the B--V Colors of Their Parent Galaxies, and the Value of H
Statistical connections between the properties of Type Ia supernovae (SNe Ia)
and the B--V colors of their parent galaxies are established. Compared to SNe
Ia in blue galaxies [B-V\la0.75], SNe Ia in redder galaxies have (1) a wider
dispersion in the blueshifts of their Si II 6355 absorption features,
ten days after maximum light; (2) more rapidly declining light curves; and (3)
lower luminosities. Even when the spectroscopically peculiar, very subluminous
SNe Ia such as SN 1991bg are disregarded, SNe Ia in red galaxies are less
luminous than those in blue galaxies by about 0.3 magnitudes.
When SNe Ia that are thought to have been significantly extinguished by dust
in their parent galaxies are disregarded, those in blue galaxies have
observational absolute--magnitude dispersions of only =0.20
and =0.17, which implies that their intrinsic
absolute--magnitude dispersions are very small. We use six SNe Ia whose
absolute magnitudes have been calibrated by means of Cepheids, which also
indicate that the intrinsic absolute--magnitude dispersions of SNe Ia in blue
galaxies are very small, to calibrate SNe Ia in blue galaxies and obtain . This value is in excellent agreement with
that obtained by Saha et al. (1995b), in spite of the fact that they do not
take into account any dependence of SN Ia absolute magnitude on the nature of
the parent galaxy.
Some implications of the statistical connections between SNe Ia and the
colors of their parent galaxies, for identifying the progenitor binary systems
of SNe Ia and for using high--redshift SNe Ia to measure q, are briefly
discussed.Comment: LaTeX file, AASTeX4 style, 2 Tables and 4 Figures included
separately. Postscript file available from http://www.nhn.uoknor.edu/~baron
Color patterns in the Kuiper Belt: A possible primordial origin
As a result of our continuing photometric survey, we report here optical colors for 36 Kuiper Belt objects, increasing our sample size to 91 objects. We find that certain dynamical classes of objects exhibit distinctive colors—21 out of 21 objects on small-inclination and small-eccentricity orbits with perihelion distances larger than 40 AU exhibit red surface colors (B-R > 1.5), while 17 out of 20 objects on large-inclination and large-eccentricity orbits with aphelion distances larger than 70 AU exhibit gray surface colors (B-R < 1.5). Our observations are consistent with a primordial origin for Kuiper Belt surface colors, if we assume that gray objects formed closer to the Sun than red objects, and as Neptune migrated outward it scattered gray objects onto dynamically hot orbits. By this model, the contrasting dynamically cold and red objects beyond 40 AU remained far enough away from Neptune that they were never perturbed by the planet
Photometry of the trans-neptunian object 1993 SC.
We obtained broadband photometry of the Trans-Neptunian Object 1993 SC with the Steward Observatory 1.5-m telescope near Mt. Bigelow, Arizona and the Lunar and Planetary Laboratory CCD on 8 October 1996. 1993 SC exhibited a constant brightness (V = 22.67) with a 1 sigma scatter about the average of 0.06 magnitudes during a five hour interval. In addition, we obtained observations of 1993 SC with the Steward Observatory 2.3-m telescope on Kitt Peak, Arizona during 24 - 27 November 1995. Once again 1993 SC exhibited a constant brightness (V = 22.73) with a 1 sigma scatter about the average of 0.04 magnitudes. If 1993 SC has a lightcurve, the amplitude must be at the level of 0.12 magnitudes or less. If the obliquity of 1993 SC is near zero degrees, then 1993 SC is spherical with a semi-major to semi-minor axis ratio less than or equal to 1.12. A spherical nature for 1993 SC may be the result of self gravity exceeding the tensile strength of the material in the interior of 1993 SC. If the obliquity of 1993 SC is large, then 1993 SC could have an irregular shape. The steady intrinsic brightness for 1993 SC suggests that the object has a relatively uniform surface albedo. Our photometry and the assumption of a comet-like albedo (0.04) indicates that the diameter of 1993 SC is ~ 240 km
Analysis of the rotational properties of Kuiper belt objects
We use optical data on 10 Kuiper Belt objects (KBOs) to investigate their
rotational properties. Of the 10, three (30%) exhibit light variations with
amplitude delta_m >= 0.15 mag, and 1 out of 10 (10%) has delta_m >= 0.40 mag,
which is in good agreement with previous surveys. These data, in combination
with the existing database, are used to discuss the rotational periods, shapes,
and densities of Kuiper Belt objects. We find that, in the sampled size range,
Kuiper Belt objects have a higher fraction of low amplitude lightcurves and
rotate slower than main belt asteroids. The data also show that the rotational
properties and the shapes of KBOs depend on size. If we split the database of
KBO rotational properties into two size ranges with diameter larger and smaller
than 400 km, we find that: (1) the mean lightcurve amplitudes of the two groups
are different with 98.5% confidence, (2) the corresponding power-law shape
distributions seem to be different, although the existing data are too sparse
to render this difference significant, and (3) the two groups occupy different
regions on a spin period vs. lightcurve amplitude diagram. These differences
are interpreted in the context of KBO collisional evolution.Comment: 15 pages, 14 figures, LaTeX. Astronomical Journal in pres
Compliant Electric Actuators Based on Handed Shearing Auxetics
In this paper, we explore a new class of electric motor-driven compliant actuators based on handed shearing auxetic cylinders. This technique combines the benefits of compliant bodies from soft robotic actuators with the simplicity of direct coupling to electric motors. We demonstrate the effectiveness of this technique by creating linear actuators, a four degree-of-freedom robotic platform, and a soft robotic gripper. We compare the soft robotic gripper against a state of the art pneumatic soft gripper, finding similar grasping performance in a significantly smaller and more energy-efficient package.Boeing CompanyNational Science Foundation (U.S.) (grant numbers NSF IIS- 1226883)National Science Foundation (U.S.) (grant numbers NSF CCF-1138967
Ice mineralogy across and into the surfaces of Pluto, Triton, and Eris
We present three near-infrared spectra of Pluto taken with the Infrared Telescope Facility and SpeX, an optical spectrum of Triton taken with the MMT and the Red Channel Spectrograph, and previously published spectra of Pluto, Triton, and Eris. We combine these observations with a two-phase Hapke model and gain insight into the ice mineralogy on Pluto, Triton, and Eris. Specifically, we measure the methane-nitrogen mixing ratio across and into the surfaces of these icy dwarf planets. In addition, we present a laboratory experiment that demonstrates it is essential to model methane bands in spectra of icy dwarf planets with two methane phases—one highly diluted by nitrogen and the other rich in methane. For Pluto, we find bulk, hemisphere-averaged, methane abundances of 9.1% ± 0.5%, 7.1% ± 0.4%, and 8.2% ± 0.3% for sub-Earth longitudes of 10°, 125°, and 257°. Application of the Wilcoxon rank sum test to our measurements finds these small differences are statistically significant. For Triton, we find bulk, hemisphere-averaged, methane abundances of 5.0% ± 0.1% and 5.3% ± 0.4% for sub-Earth longitudes of 138° and 314°. Application of the Wilcoxon rank sum test to our measurements finds the differences are not statistically significant. For Eris, we find a bulk, hemisphere-averaged, methane abundance of 10% ± 2%. Pluto, Triton, and Eris do not exhibit a trend in methane-nitrogen mixing ratio with depth into their surfaces over the few centimeter range probed by these observations. This result is contrary to the expectation that since visible light penetrates deeper into a nitrogen-rich surface than the depths from which thermal emission emerges, net radiative heating at depth would drive preferential sublimation of nitrogen leading to an increase in the methane abundance with depth
Methane and Nitrogen Abundances On Pluto and Eris
We present spectra of Eris from the MMT 6.5 meter telescope and Red Channel
Spectrograph (5700-9800 angstroms; 5 angstroms per pix) on Mt. Hopkins, AZ, and
of Pluto from the Steward Observatory 2.3 meter telescope and Boller and
Chivens spectrograph (7100-9400 angstroms; 2 angstroms per pix) on Kitt Peak,
AZ. In addition, we present laboratory transmission spectra of methane-nitrogen
and methane-argon ice mixtures. By anchoring our analysis in methane and
nitrogen solubilities in one another as expressed in the phase diagram of
Prokhvatilov and Yantsevich (1983), and comparing methane bands in our Eris and
Pluto spectra and methane bands in our laboratory spectra of methane and
nitrogen ice mixtures, we find Eris' bulk methane and nitrogen abundances are
about 10% and about 90%, and Pluto's bulk methane and nitrogen abundances are
about 3% and about 97%. Such abundances for Pluto are consistent with values
reported in the literature. It appears that the bulk volatile composition of
Eris is similar to the bulk volatile composition of Pluto. Both objects appear
to be dominated by nitrogen ice. Our analysis also suggests, unlike previous
work reported in the literature, that the methane and nitrogen stoichiometry is
constant with depth into the surface of Eris. Finally, we point out that our
Eris spectrum is also consistent with a laboratory ice mixture consisting of
40% methane and 60% argon. Although we cannot rule out an argon rich surface,
it seems more likely that nitrogen is the dominant species on Eris because the
nitrogen ice 2.15 micron band is seen in spectra of Pluto and Triton.Comment: The manuscript has 44 pages, 15 figures, and four tables. It will
appear in the Astrophysical Journa
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