We report on g-, r-, and i-band observations of the Interstellar Object 1I/'Oumuamua (1I) taken on 2017 October 29 from 04:28 to 08:40 UTC by the Apache Point Observatory (APO) 3.5 m telescope's ...ARCTIC camera. We find that 1I's colors are and , consistent with visible spectra and most comparable to the population of solar system C/D asteroids, Trojans, or comets. We find no evidence of any cometary activity at a heliocentric distance of 1.46 au, approximately 1.5 months after 1I's closest approach distance to the Sun. Significant brightness variability was seen in the r observations, with the object becoming notably brighter toward the end of the run. By combining our APO photometric time series data with the Discovery Channel Telescope data of Knight et al., taken 20 hr later on 2017 October 30, we construct an almost complete lightcurve with a most probable single-peaked lightcurve period of . Our results imply a double-peaked rotation period of 8.1 0.02 hr, with a peak-to-trough amplitude of 1.5-2.1 mag. Assuming that 1I's shape can be approximated by an ellipsoid, the amplitude constraint implies that 1I has an axial ratio of 3.5-10.3, which is strikingly elongated. Assuming that 1I is rotating above its critical break up limit, our results are compatible with 1I having modest cohesive strength and may have obtained its elongated shape during a tidal distortion event before being ejected from its home system.
We present the determination of the geometric R-band albedos of two main-belt comet (MBC) nuclei based on data from the Spitzer Space Telescope and a number of ground-based optical facilities. For ...133P/Elst-Pizarro, we find an albedo of pR = 0.05 ± 0.02 and an effective radius of re = 1.9 ± 0.3 km (estimated semiaxes of a ~ 2.3 km and b ~ 1.6 km). For 176P/LINEAR, we find an albedo of pR = 0.06 ± 0.02 and an effective radius of re = 2.0 ± 0.2 km (estimated semiaxes of a ~ 2.6 km and b ~ 1.5 km). In terms of albedo, 133P and 176P are similar to each other and are typical of other Themis family asteroids, C-class asteroids, and other comet nuclei. We find no indication that 133P and 176P are compositionally unique among other dynamically similar (but inactive) members of the Themis family, in agreement with previous assertions that the two objects most likely formed in situ. We also note that low albedo (pR < 0.075) remains a consistent feature of all cometary (i.e., icy) bodies, whether they originate in the inner solar system (the MBCs) or in the outer solar system (all other comets).
1I/'Oumuamua is the first confirmed interstellar body in our solar system. Here we report on observations of 'Oumuamua made with the Spitzer Space Telescope on 2017 November 21-22 (UT). We integrated ...for 30.2 hr at 4.5 m (IRAC channel 2). We did not detect the object and place an upper limit on the flux of 0.3 Jy (3 ). This implies an effective spherical diameter less than 98, 140, 440 m and albedo greater than 0.2, 0.1, 0.01 under the assumption of low, middle, or high thermal beaming parameter , respectively. With an aspect ratio for 'Oumuamua of 6:1, these results correspond to dimensions of 240:40, 341:57, 1080:180 m, respectively. We place upper limits on the amount of dust, CO, and CO2 coming from this object that are lower than previous results; we are unable to constrain the production of other gas species. Both our size and outgassing limits are important because 'Oumuamua's trajectory shows non-gravitational accelerations that are sensitive to size and mass and presumably caused by gas emission. We suggest that 'Oumuamua may have experienced low-level post-perihelion volatile emission that produced a fresh, bright, icy mantle. This model is consistent with the expected value and implied high-albedo value for this solution, but, given our strict limits on CO and CO2, requires another gas species-probably H2O-to explain the observed non-gravitational acceleration. Our results extend the mystery of 'Oumuamua's origin and evolution.
Abstract
We present a dynamical study of 39 active Centaurs and 17 high-perihelion (
q
> 4.5 au) Jupiter-family comets (JFCs) with a focus on investigating recent orbital changes as potential ...triggers for comet-like activity. We have identified a common feature in the recent dynamical histories of all active Centaurs and JFCs in our sample that is not present in the history of the majority of inactive population members: a sharp decrease in semimajor axis and eccentricity occurring within the past several hundred years prior to observed activity. We define these rapid orbital changes as “
a
-jumps.” Our results indicate that these orbital reshaping events lead to shorter orbital periods and subsequently greater average per-orbit heating of Centaur nuclei. We suggest that the
a
-jumps could therefore be a major trigger of cometary activity on Centaurs and JFCs. Our results further imply that analyses of the recent dynamical histories could be used to identify objects that are currently active or may become active soon, where we have identified three such Centaurs with recent
a
-jumps that should be considered high-priority targets for observational monitoring to search for activity.
Albedos of Small Jovian Trojans Fernández, Yanga R; Jewitt, David; Ziffer, Julie E
The Astronomical journal,
07/2009, Letnik:
138, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present thermal observations of 44 Jovian Trojan asteroids with diameters D ranging from 5 to 24 km. All objects were observed at a wavelength of 24 mm with the Spitzer Space Telescope. ...Measurements of the thermal emission and of scattered optical light, mostly from the University of Hawaii 2.2 m Telescope, together allow us to constrain the diameter and geometric albedo of each body. We find that the median R-band albedo of these small Jovian Trojans is about 0.12, much higher than that of 'large' Trojans with D>57 km (0.04). Also the range of albedos among the small Trojans is wider. The small Trojans' higher albedos are also glaringly different from those of cometary nuclei, which match our sample Trojans in diameter, however, they roughly match the spread of albedos among (much larger) Centaurs and trans-Neptunian objects. We attribute the Trojan albedos to an evolutionary effect: the small Trojans are more likely to be collisional fragments and so their surfaces would be younger. A younger surface means less cumulative exposure to the space environment, which suggests that their surfaces would not be as dark as those of the large, primordial Trojans. In support of this hypothesis is a statistically significant correlation of higher albedo with smaller diameter in our sample alone and in a sample that includes the larger Trojans. This correlation of albedo and radius implies that the true size distribution of small Trojans is shallower than the visible magnitude distribution alone would suggest, and that there are approximately half the Trojans with D>1 km than previously estimated.
2013 FY27 is the ninth intrinsically brightest Trans-Neptunian Object (TNO). We used ALMA at thermal wavelengths and Magellan in the optical to determine 2013 FY27's size and albedo for the first ...time and compare it to other dwarf planets. We found 2013 FY27 has a geometric albedo of and effective diameter of km. This puts 2013 FY27 in the transition region between the largest TNOs that have higher albedos and densities than smaller TNOs. No short-term light curve was found, with variations <0.06 0.02 mag over hours and days. The Sloan colors of 2013 FY27 are g−r = 0.76 0.02 and r−i = 0.31 0.03 mag, giving a moderately red color. This is different than the neutral or ultra-red colors found for the 10 largest TNOs, making 2013 FY27 one of the largest moderately red TNOs, which are only seen, and in abundance, at diameters less than 800 km. This suggests something different might be associated with TNOs larger than 800 km. Moderately red colors might indicate old or ice-poor surfaces with TNOs larger than 800 km having fresher or more volatile-rich surfaces. TNOs larger than 800 km could be more differentiated, giving them different surface compositions. A satellite at 0 17 and 3.0 0.2 mag fainter than 2013 FY27 was found through Hubble Space Telescope observations. Almost all the largest TNOs have satellites, which now includes 2013 FY27. Assuming a similar albedo, the satellite is ∼186 km in diameter, making the primary km.
•We analyzed Spitzer IRAC, MIPS, and IRS observations of Comet 29P.•We applied a NEATM to extracted nucleus spectral flux density measurements.•We measured an effective radius R=30.2-2.9+3.7km and an ...infrared beaming parameter η=0.99-0.19+0.26.•Using IRS SED we modeled the come dust composition of 29P.
We present a new analysis of Spitzer observations of Comet 29P/Schwassmann–Wachmann 1 taken on UT 2003 November 21, 23, and 24, similar to a previous investigation of the observations (Stansberry et al., 2004), but using the most recent Spitzer data pipeline products and intensive image processing techniques. Analysis of images from the IRAC 5.8 and 8.0μm bands and the MIPS 24.0 and 70.0μm bands resulted in photometry measurements of the nucleus after a suite of coma modeling and removal processes were implemented. SW1 was not identified in the 5.8μm image from the previous work so its incorporation into this analysis is entirely new. Using the Near Earth Asteroid Thermal Model (Harris, 1998) resulted in a nucleus radius measurement of R=30.2-2.9+3.7km and an infrared beaming parameter value of η=0.99-0.19+0.26. We also measured an infrared geometric albedo, p5.8=0.5±0.5. Extrapolating a 0.04V-band albedo and using a normalized reflectivity gradient S′=14.94±1.09 % (1000Å)−1 (Duffard, R., et al. 2014. Astron. Astrophys. 564, A92) we recover an infrared albedo of p5.8=0.31 in the near infrared consistent with the value recovered from thermal modeling. The dust composition extracted from IRS spectra are very comet-like, containing mainly amorphous ferromagnesian silicates (but with a minority of crystalline silicates as well), water ice, and metal sulfides.
We present analysis of Hubble Space Telescope observations of Centaur 29P/Schwassmann-Wachmann 1 (SW1) while in outburst to characterize the outburst coma and place constraints on the nucleus' spin ...state. The observations consist of Wide Field and Planetary Camera 2 (WFPC2) images from Cycle 5, GO-5829 acquired on UT 1996 March 11.3 and 12.1, which serendipitously imaged the Centaur shortly after a major outburst. A multi-component coma was detected consisting of an expanding outburst dust coma with complex morphology possessing an east-west asymmetry and north-south symmetry contained within 5″ (∼19,000 km) of the nucleus, the residual dust shell of an earlier UT 1996 February outburst, and a nearly circular coma with underlying quiescent activity level detectable to ∼70″ (∼267,000 km) away from the nucleus. Photometry of the calibrated WFPC2 images resulted in an equivalent R-band magnitude of 12.86 0.02 for a measured 5″ radius aperture and an estimated (2.79 0.05) × 108 kg for the lower limit of dust material emitted during the outburst. No appreciable evolution of morphological features, indicating signatures of nuclear rotation, was detected between the two imaging epochs. The observations were modeled using a 3D Monte Carlo coma model to place constraints on the nucleus' rotation state. Modeling indicated that the morphology is representative of a non-isotropic ejection of dust emitted during a single outburst event with a duration of the order of hours from a single source region corresponding to ∼1% of the surface area. A spin period with lower limit of the order of days is suggested to reproduce the coma morphology seen in the observations.
We use NEOWISE data from the four-band and three-band cryogenic phases of the Wide-field Infrared Survey Explorer mission to constrain size distributions of the comet populations and debias ...measurements of the short- and long-period comet (LPC) populations. We find that the fit to the debiased LPC population yields a cumulative size−frequency distribution (SFD) power-law slope (β) of −1.0 0.1, while the debiased Jupiter-family comet (JFC) SFD has a steeper slope with β = −2.3 0.2. The JFCs in our debiased sample yielded a mean nucleus size of 1.3 km in diameter, while the LPCs' mean size is roughly twice as large, 2.1 km, yielding mean size ratios ( ) that differ by a factor of 1.6. Over the course of the 8 months of the survey, our results indicate that the number of LPCs passing within 1.5 au are a factor of several higher than previous estimates, while JFCs are within the previous range of estimates of a few thousand down to sizes near 1.3 km in diameter. Finally, we also observe evidence for structure in the orbital distribution of LPCs, with an overdensity of comets clustered near 110° inclination and perihelion near 2.9 au that is not attributable to observational bias.
Although solar-analog stars have been studied extensively over the past few decades, most of these studies have focused on visible wavelengths, especially those identifying solar-analog stars to be ...used as calibration tools for observations. As a result, there is a dearth of well-characterized solar analogs for observations in the near-infrared, a wavelength range important for studying solar system objects. We present 184 stars selected based on solar-like spectral type and V−J and V−K colors whose spectra we have observed in the 0.8-4.2 m range for calibrating our asteroid observations. Each star has been classified into one of three ranks based on spectral resemblance to vetted solar analogs. Of our set of 184 stars, we report 145 as reliable solar-analog stars, 21 as solar analogs usable after spectral corrections with low-order polynomial fitting, and 18 as unsuitable for use as calibration standards owing to spectral shape, variability, or features at low to medium resolution. We conclude that all but five of our candidates are reliable solar analogs in the longer wavelength range from 2.5 to 4.2 m. The average colors of the stars classified as reliable or usable solar analogs are V−J = 1.148, V−H = 1.418, and V−K = 1.491, with the entire set being distributed fairly uniformly in R.A. across the sky between −27° and +67° in decl.
PDF
