We study the internal radial gradients of stellar population properties within 1.5 Re and analyse the impact of galaxy environment. We use a representative sample of 721 galaxies with masses ranging ...between 10 super( 9) M... and 10 super( 11.5) M... from the SDSS-IV survey MaNGA. We split this sample by morphology into early-type and late-type galaxies. Using the full spectral fitting code FIREFLY, we derive the light and mass-weighted stellar population properties, age and metallicity, and calculate the gradients of these properties. We use three independent methods to quantify galaxy environment, namely the Nth nearest neighbour, the tidal strength parameter Q and distinguish between central and satellite galaxies. In our analysis, we find that early-type galaxies generally exhibit shallow light-weighted age gradients in agreement with the literature and mass-weighted median age gradients tend to be slightly positive. Late-type galaxies, instead, have negative light-weighted age gradients. We detect negative metallicity gradients in both early- and late-type galaxies that correlate with galaxy mass, with the gradients being steeper and the correlation with mass being stronger in late-types. We find, however, that stellar population gradients, for both morphological classifications, have no significant correlation with galaxy environment for all three characterizations of environment. Our results suggest that galaxy mass is the main driver of stellar population gradients in both early and late-type galaxies, and any environmental dependence, if present at all, must be very subtle. (ProQuest: ... denotes formulae/symbols omitted.)
The Wide-field Infrared Survey Explorer (WISE) observed 52 Centaurs and scattered disk objects (SDOs) in the thermal infrared, including 15 new discoveries. We present analyses of these observations ...to estimate sizes and mean optical albedos. We find mean albedos of 0.08 + or - 0.04 for the entire data set. Thermal fits yield average beaming parameters of 0.9 + or - 0.2 that are similar for both SDO and Centaur sub-classes. Biased cumulative size distributions yield size-frequency distribution power law indices of ~-1.7 + or - 0.3. The data also reveal a relation between albedo and color at the 3sigma level. No significant relation between diameter and albedos is found.
ABSTRACT The 163 comets observed during the WISE/NEOWISE prime mission represent the largest infrared survey to date of comets, providing constraints on dust, nucleus size, and CO + CO2 production. ...We present detailed analyses of the WISE/NEOWISE comet discoveries, and discuss observations of the active comets showing 4.6 m band excess. We find a possible relation between dust and CO + CO2 production, as well as possible differences in the sizes of long and short period comet nuclei.
We report results based on mid-infrared photometry of comet 103P/Hartley 2 taken during 2010 May 4-13 (when the comet was at a heliocentric distance of 2.3 AU, and an observer distance of 2.0 AU) by ...the Wide-field Infrared Survey Explorer. Photometry of the coma at 22 Delta *mm and data from the University of Hawaii 2.2 m telescope obtained on 2010 May 22 provide constraints on the dust particle size distribution, d log n/d log m, yielding power-law slope values of alpha = --0.97 ? 0.10, steeper than that found for the inbound particle fluence during the Stardust encounter of comet 81P/Wild 2. The extracted nucleus signal at 12 Delta *mm is consistent with a body of average spherical radius of 0.6 ? 0.2 km (one standard deviation), assuming a beaming parameter of 1.2. The 4.6 Delta *mm band signal in excess of dust and nucleus reflected and thermal contributions may be attributed to carbon monoxide or carbon dioxide emission lines and provides limits and estimates of species production. Derived carbon dioxide coma production rates are 3.5(? 0.9) X 1024 molecules per second. Analyses of the trail signal present in the stacked image with an effective exposure time of 158.4 s yields optical-depth values near 9 X 10--10 at a delta mean anomaly of 0.2 deg trailing the comet nucleus, in both 12 and 22 Delta *mm bands. A minimum chi-squared analysis of the dust trail position yields a beta-parameter value of 1.0 X 10--4, consistent with a derived mean trail-grain diameter of 1.1/ Delta *r cm for grains of Delta *r g cm--3 density. This leads to a total detected trail mass of at least 4 X 1010 Delta *r kg.
We report results based on mid-infrared photometry of five active main belt objects (AMBOs) detected by the Wide-field Infrared Survey Explorer (WISE) spacecraft. Four of these bodies, P/2010 R2 (La ...Sagra), 133P/Elst-Pizarro, (596) Scheila, and 176P/LINEAR, showed no signs of activity at the time of the observations, allowing the WISE detections to place firm constraints on their diameters and albedos. Geometric albedos were in the range of a few percent, and on the order of other measured comet nuclei. P/2010 A2 was observed on 2010 April 2-3, three months after its peak activity. Photometry of the coma at 12 and 22 mu m combined with ground-based visible-wavelength measurements provides constraints on the dust particle mass distribution (PMD), dlog n/dlog m, yielding power-law slope values of alpha = -0.5 + or - 0.1. This PMD is considerably more shallow than that found for other comets, in particular inbound particle fluence during the Stardust encounter of comet 81P/Wild 2. It is similar to the PMD seen for 9P/Tempel 1 in the immediate aftermath of the Deep Impact experiment. Upper limits for CO sub(2) and CO production are also provided for each AMBO and compared with revised production numbers for WISE observations of 103P/Hartley 2.
On 2010 January 18-19 and June 28-29, the Wide-field Infrared Survey Explorer (WISE) spacecraft imaged the Rosetta mission target, comet 67P/Churyumov-Gerasimenko. We present a preliminary analysis ...of the images, which provide a characterization of the dust environment at heliocentric distances similar to those planned for the initial spacecraft encounter, but on the outbound leg of its orbit rather than the inbound. Broadband photometry yields low levels of CO sub(2) production at a comet heliocentric distance of 3.32 AU and no detectable production at 4.18 AU. We find that at these heliocentric distances, large dust grains with mean grain diameters on the order of a millimeter or greater dominate the coma and evolve to populate the tail. This is further supported by broadband photometry centered on the nucleus, which yield an estimated differential dust particle size distribution with a power-law relation that is considerably shallower than average. We set a 3sigma upper limit constraint on the albedo of the large-grain dust at < or =, slant0.12. Our best estimate of the nucleus radius (1.82 + or - 0.20 km) and albedo (0.04 + or - 0.01) are in agreement with measurements previously reported in the literature.
► We conducted observations of Asteroid 1996 FG3 from the NASA IRTF. ► Absorptions attributed to OH in minerals seen on multiple nights. ► Absorptions consistent with what is seen on main-belt C ...asteroids. ► Existence of OH in minerals constrains heating seen at current surface. ► Fresh material likely available on FG3’s surface for sampling missions.
We present observations of the binary near-Earth Asteroid (175706) 1996 FG3 in the 2–4μm spectral region, obtained on multiple nights using the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We find evidence for an absorption band of ∼5–10% (depending on the night and details of continuum choice), diagnostic for hydrated/hydroxylated minerals on the asteroid surface. This demonstrates that the optical surface of 1996 FG3 has not been heated to dehydrating temperatures. Sample-return missions targeting 1996 FG3 will likely find relatively fresh areas for sampling.
The excited spin state of Comet 2P/Encke Belton, Michael J.S.; Samarasinha, Nalin H.; Fernández, Yan R. ...
Icarus (New York, N.Y. 1962),
05/2005, Letnik:
175, Številka:
1
Journal Article
Recenzirano
Ways to rationalize the different periods (e.g., 15.08 h, Luu and Jewitt, 1990, Icarus 86, 69–81; 11.01 h, Fernández et al., 2004, Icarus, in this issue; Lowry et al., 2003, Lunar Planet. Sci. XXXIV, ...Abstract 2056) seen in near aphelion R-band light curves of Comet 2P/Encke are explored. We show that the comet is usually active at aphelion and it's observed light curves contain signal from both the nucleus and an unresolved coma. The coma contribution to the observed brightness is generally found to dominate with the nucleus providing from 28 to 87% of the total brightness. The amplitude of the observed
variations cannot be explained by the nucleus alone and are due to coma activity. We show that some seven periodicities exist in the observed light curves at various times and that this is likely the result of an active nucleus spinning in an excited spin state. The changing periodicities are probably due to changes in the relative strengths of the active areas. We work out possible excited states based on experience with model light curves and by using an analogy to light curve observations of Comet 1P/Halley for which the spin state has been separately determined from spacecraft observations. There is a possibility of a fully relaxed principal axis spin state (0.538 d
−1;
P
=
44.6
h
) but, because it provides a poorer fit to the observed periodicities than the best fit excited state together with the absence of a peak near 1.08 d
−1 (
2
f
φ
) in the frequency spectrum of the Fernández et al. (2000, Icarus 147, 145–160) thermal IR lightcurve, we consider it unlikely. Both SAM and LAM excited states are allowed by the underlying periodicities and additional information is needed to choose between these. Our choice of a low excitation SAM state, i.e., one in which the instantaneous spin axis nutates around the total angular momentum vector in a motion that is characterized by limited angular oscillations around the long axis, is based on Sekanina's (1988, Astron J. 95, 911–924, 1988, Astron. J. 96, 1455–1475) interpretation of the fan coma that this comet often displays. We argue that possible LAM states are excluded either because they are too difficult to excite or because they would be inconsistent with the formation of the observed fan morphology. Two possible SAM states emerge that provide good fits to the observed periodicities, one with a precessional frequency for the long axis about the total angular momentum vector of 1.614 d
−1 (
P
ϕ
=
14.9
h
) and an oscillation frequency around the long axis of 0.539 d
−1 (
P
ψ
=
44.5
h
) and a second with a precessional frequency of 2.162 d
−1 (
P
ϕ
=
11.1
h
) combined with an oscillation around the long axis of 0.502 d
−1 (
P
ψ
=
47.8
h
). While either solution is possible, the latter is, in a least squares sense, more likely to be the actual spin state. In both cases the direction of the total angular momentum vector (
α
M
,
δ
M
J
2000
=
198.6
,
−
0.3
deg
) is assumed to be defined by the evolving geometry and morphology of the coma (Sekanina, 1988, Astron J. 95, 911–924, 1988, Astron. J. 96, 1455–1475; Festou and Barale, 2000, Astron J. 119, 3119–3132). We discuss the possible locations of the primary active areas found by Sekanina (1988, Astron J. 95, 911–924, 1988, Astron. J. 96, 1455–1475) and, while they are at high cometographic latitudes, they do not have to be physically located close the region were the axis of maximum moment of inertia pierces the surface (i.e., at high cometocentric latitude). We offer a new interpretation of the 10.7 μm data by Fernández et al. (2000, Icarus 147, 145–160) which yields an axial ratio
a
/
b
=
2.04
. This, with the two SAM states that we have found, requires that
b
/
c
>
1.18
or >1.09 implying a significant asymmetry in the shape of the elongated nucleus. For the observed fan morphology to be maintained, the true axial ratio
b
/
c
cannot be much larger than these limiting values otherwise the amplitude of the oscillation about the long axis becomes too large and the fan morphology would be destroyed. The precise phasing of the spin modes, i.e., the value of the Euler angles at a particular time, is not determinable from the current data set, but a set of well sampled thermal infrared observations of the nucleus covering many periods and a wide range of observing geometries could provide this information in the future as well as clearly distinguishing between the two excited spin states.
The 163 comets observed during the WISE/NEOWISE prime mission represent the largest infrared survey to date of comets, providing constraints on dust, nucleus size, and CO + CO{sub 2} production. We ...present detailed analyses of the WISE/NEOWISE comet discoveries, and discuss observations of the active comets showing 4.6 μm band excess. We find a possible relation between dust and CO + CO{sub 2} production, as well as possible differences in the sizes of long and short period comet nuclei.
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