Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userColor variations of Comet C/2013 UQ4 (Catalina)
95
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report observations of color in the inner coma of Comet C/2013 UQ4 (Catalina) with the broadband B and R filters. We find significant temporal variations of the color slope, ranging from -12.67 $pm$ 8.16 % per 0.1~$mu$m up to $35.09 pm 11.7$ % per 0.1~$mu$m.It is significant that the comet changes color from red to blue over only a two-day period. Such dispersion cannot be characterized with an average color slope. We also observe Comet C/2013 UQ4 (Catalina) in infrared using Spitzer and find no significant CO/CO$_{2}$ gaseous species in its coma. Therefore, we classify Comet C/2013 UQ4 (Catalina) as a dust-rich comet and attribute the measured color slope to its dust. We analyze the color slope using the model of agglomerated debris particles and conclude that the C/2013 UQ4 coma was chemically heterogeneous, consisting of at least two components. The first component producing the bluest color is consistent with Mg-rich silicates. There are three different options for the second component producing the reddest color. This color is consistent with either Mg-Fe silicates, kerogen type II, or organic matter processed with a low dose of UV radiation.
rate research
Read More
We present IRTF/SpeX and NEOWISE observations of the dynamically new comet C/2013 US$_{10}$ (Catalina), hereafter US10, from 5.8 au inbound, to near perihelion at 1.3 au, and back to 5.0 au outbound. We detect water ice in the coma of US10, assess and monitor the physical properties of the ice as insolation varies with heliocentric distance, and investigate the relationship between water ice and CO$_{2}$. This set of measurements is unique in orbital coverage and can be used to infer the physical evolution of the ice and, potentially, the nucleus composition. We report (1) nearly identical near-infrared spectroscopic measurements of the coma at $-$5.8 au, $-$5.0 au, +3.9 au (where $<$0 au indicates pre-perihelion epochs), all presenting evidence of water-ice grains, (2) a dust-dominated coma at 1.3 au and 2.3 au and, (3) an increasing CO$_{2}$/$Afrho$ ratio from $-$4.9 au to 1.8 au. We propose that sublimation of the hyper-volatile CO$_{2}$ is responsible for dragging water-ice grains into the coma throughout the orbit. Once in the coma, the observability of the water-ice grains is controlled by the ice grain sublimation lifetime, which seems to require some small dust contaminant (i.e., non-pure ice grains). At |R$_{h}$|>=3.9 au, the ice grains are long-lived and may be unchanged since leaving the comet nucleus. We find the nucleus of comet US10 is made of, among other components, $sim$1-micron water-ice grains containing up to 1% refractory materials.
We present an optical and near-infrared (hereafter NIR) polarimetric study of a comet C/2013 US10 (Catalina) observed on UT 2015 December 17-18 at phase angles of $alpha$=52.1 deg - 53.1 deg. Additionally, we obtained an optical spectrum and multi-band images to examine the influence of gas emission. We find that the observed optical signals are significantly influenced by gas emission, that is, the gas-to-total intensity ratio varies from 5 to 30 % in the $R_{rm C}$ and 3 to 18 % in the $I_{rm C}$ bands, depending on the position in the coma. We derive the `gas-free dust polarization degrees of 13.8$pm$1.0 % in the $R_{rm C}$ and 12.5$pm$1.1 % in the $I_{rm C}$ bands and a gray polarimetric color, i.e., -8.7$pm$9.9 % $mu mathrm{m}$$^{-1}$ in optical and 1.6$pm$0.9 % $mu mathrm{m}$$^{-1}$ in NIR. The increments of polarization obtained from the gas correction show that the polarimetric properties of the dust in this low-polarization comet are not different from those in high-polarization comets. In this process, the cometocentric distance dependence of polarization has disappeared. We also find that the $R_{rm C}$-band polarization degree of the southeast dust tail, which consists of large dust particles (100 $mu mathrm{m}$ - 1 mm), is similar to that in the outer coma where small and large ones are mixed. Our study confirms that the dichotomy of cometary polarization does not result from the difference of dust properties, but from depolarizing gas contamination. This conclusion can provide a strong support for similarity in origin of comets.
We observed Comet C/Siding Spring using the Hubble Space Telescope (HST) during its close approach to Mars. The high spatial resolution images obtained through the F689M, F775W, and F845M filters reveal the characteristics of the dust coma. The dust production rate of C/Siding Spring, quantified by $Afrho$, is 590$pm$30, 640$pm$30, and 670$pm$30 cm in a 420 km-radius aperture at 38$^circ$ solar phase angle through the three filters, respectively, consistent with other observations at similar time and geometry, and with model predictions based on earlier measurements. The dust expansion velocity is ~150-250 m s$^{-1}$ for micron-sized dust grains, similar to the speeds found for other comets. The coma has a color slope of (5.5$pm$1.5)%/100 nm between 689 and 845 nm, similar to previous HST measurements at comparable aperture sizes, consistent with the lack of color dependence on heliocentric distance for almost all previously observed active comets. The rotational period of the nucleus of C/Siding Spring is determined from the periodic brightness variation in the coma to be 8.00$pm$0.08 hours, with no excited rotational state detected. The dust coma shows a broad and diffuse fan-shaped feature in the sunward direction, with no temporal morphological variation observed. The projected orientation of the dust feature, combined with the previous analysis of the coma morphology and other characteristics, suggests secular activity evolution of the comet in its inner solar system passage as one previously observed active region turns off whereas new regions exposed to sunlight due to seasonal illumination change.
Comet C/2013 A1 (siding Spring) will experience a high velocity encounter with Mars on October 19, 2014 at a distance of 135,000 km +- 5000 km from the planet center. We present a comprehensive analysis of the trajectory of both the comet nucleus and the dust tail. The nucleus of C/2013 A1 cannot impact on Mars even in the case of unexpectedly large nongravitational perturbations. Furthermore, we compute the required ejection velocities for the dust grains of the tail to reach Mars as a function of particle radius and density and heliocentric distance of the ejection. A comparison between our results and the most current modeling of the ejection velocities suggests that impacts are possible only for millimeter to centimeter size particles released more than 13 au from the Sun. However, this level of cometary activity that far from the Sun is considered extremely unlikely. The arrival time of these particles spans a 20-minute time interval centered at October 19, 2014 at 20:09 TDB, i.e., around the time that Mars crosses the orbital plane of C/2013 A1. Ejection velocities larger than currently estimated by a factor >2 would allow impacts for smaller particles ejected as close as 3 au from the Sun. These particles would reach Mars from 43 to 130 min after the nominal close approach epoch of the purely gravitational trajectory of the nucleus.
The Mars flyby of C/2013 A1 (Siding Spring) represented a unique opportunity for imaging a long-period comet and resolving its nucleus and rotation period. Because of the small encounter distance and the high relative velocity, the goal of successfully observing C/2013 A1 from the Mars orbiting spacecrafts posed strict accuracy requirements on the comets ephemerides. These requirements were hard to meet, as comets are known for being highly unpredictable: astrometric observations can be significantly biased and nongravitational perturbations affect comet trajectories. Therefore, even prior to the encounter, we remeasured a couple of hundred astrometric images obtained with ground-based and Earth-orbiting telescopes. We also observed the comet with the Mars Reconnaissance Orbiters High Resolution Imaging Science Experiment (HiRISE) camera on 2014 October 7. In particular, these HiRISE observations were decisive in securing the trajectory and revealed that out-of-plane nongravitational perturbations were larger than previously assumed. Though the resulting ephemeris predictions for the Mars encounter allowed observations of the comet from the Mars orbiting spacecrafts, post-encounter observations show a discrepancy with the pre-encounter trajectory. We reconcile this discrepancy by employing the Rotating Jet Model, which is a higher fidelity model for nongravitational perturbations and provides an estimate of C/2013 A1s spin pole.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
