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Register a new userVisible spectroscopy in the neighborhood of 2003 EL61
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Added by
Noemi Pinilla-Alonso
Publication date
2008
fields
Physics
and research's language is
English
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Context: The recent discovery of a group of trans-neptunian objects (TNOs) in a narrow region of the orbital parameter space and with surfaces composed of almost pure water ice, being 2003 EL61 its largest member, promises new and interesting results about the formation and evolution of the trans-neptunian belt (TNb) and the outer Solar System. Aims: The aim of this paper is to obtain information of the surface properties of two members of this group ((24835) 1995 SM55, (120178) 2003 OP32) and three potential members (2003 UZ117, (120347) 2004 SB60 and 2005 UQ513) and to use that in order to confirm or reject their association. Methods: We obtained visible spectra of five TNOs using the 3.58m Telescopio Nazionale Galileo at the Roque de los Muchachos Observatory (La Palma, Spain) Results: The spectra of the five TNOs are featureless within the uncertainties and with colors from slightly blue to red (-2< S<18%/0.1microns). No signatures of any absorption are found. Conclusions: We confirm the association of 1995 SM55 and 2003 OP32 with the group of 2003 EL61 as their spectra are almost identical to that of 2003 EL61. Only one of the three candidates, 2003 UZ117, can be considered as a possible member of the EL61-group, as its visible spectrum is compatible with a spectrum of a surface composed of almost pure water ice and no complex organics. The other two, 2004 SB60 and 2005 UQ513 are red and must be considered as interlopers.
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We present high precision, time-resolved visible and near infrared photometry of the large (diameter ~ 2500 km) Kuiper belt object (136108) 2003 EL61. The new data confirm rapid rotation at period P = 3.9155+/-0.0001 hr with a peak-to-peak photometric range (Delta m_R) = 0.29+/-0.02 mag and further show subtle but reproducible color variations with rotation. Rotational deformation of 2003 EL61 alone would give rise to a symmetric lightcurve free of color variations. The observed photometric deviations from the best-fit equilibrium model show the existence of a large surface region with an albedo and color different from the mean surface of 2003 EL61. We explore constraints on the nature of this anomalous region set by the existing data.
We present high signal precision optical reflectance spectra of the large Kuiper belt objects 2005 FY9 and 2003 EL61. The spectrum of 2005 FY9 exhibits strong CH4-ice bands. A comparison between the spectrum and a Hapke model indicates the CH4 bands are shifted 3.25 +/- 2.25A relative to pure CH4-ice, suggesting the presence of another ice component on the surface of 2005 FY9, possibly N2-ice, CO-ice, or Ar. The spectrum of 2003 EL61 is remarkably featureless. There is a hint of an O2-ice band at 5773A; however, this feature needs to be confirmed by future spectroscopic observations of 2003 EL61 with a higher continuum signal precision, sufficient to detect a second weaker O2-ice band at 6275A.
The Haumea family is currently the only identified collisional family in the Kuiper belt. We numerically simulate the long-term dynamical evolution of the family to estimate a lower limit of the familys age and to assess how the population of the family and its dynamical clustering are preserved over Gyr timescales. We find that the family is not younger than 100 Myr, and its age is at least 1 Gyr with 95% confidence. We find that for initial velocity dispersions of 50-400 m/s, approximately 20-45% of the family members are lost to close encounters with Neptune after 3.5 Gyr of orbital evolution. We apply these loss rates to two proposed models for the formation of the Haumea family, a graze-and-merge type collision between two similarly sized, differentiated KBOs or the collisional disruption of a satellite orbiting Haumea. For the graze-and-merge collision model, we calculate that >85% of the expected mass in surviving family members within 150 m/s of the collision has been identified, but that one to two times the mass of the known family members remains to be identified at larger velocities. For the satellite-break-up model, we estimate that the currently identified family members account for ~50% of the expected mass of the family. Taking observational incompleteness into account, the observed number of Haumea family members is consistent with either formation scenario at the 1 sigma level, however both models predict more objects at larger relative velocities (>150 m/s) than have been identified.
2003 EL61 is the largest member of a group of TNOs with similar orbits and unique spectra (neutral slope in the visible and the deepest water ice absorption bands ever observed in the TNb). Studying the composition of the surface of 2003 EL61 provides useful constrains on the origin of this particular group of TNOs and on the outer Solar systems history. We present visible and near-infrared spectra of 2003 EL61 obtained with the 4.2m WHT and the 3.6m TNG at the Roque de los Muchachos Observatory (Canary Islands, Spain). Near infrared spectra were obtained at different rotational phases covering almost one complete rotational period. Spectra are fitted using Hapke scattering models and constraints on the surface composition are derived. No significant variations in the spectral slope and in the depth of the water ice absorption bands at different rotational phases are evident, suggesting that the surface of 2003 EL61 is homogeneous. The scattering models show that a 1:1 intimate mixture of crystalline and amorphous water ice is the most probable composition for the surface of this TNO, and constrain the presence of other minor constituents to a maximum of 8% The derived composition suggests that: a) cryovolcanism is unlikely to be the main resurfacing process responsible for the high presence of water ice on the surface of these bodies; b) the surface is older than 10^8 yr. Any catastrophic event, like the collision suggested to be the origin of this population, had to happen at least 10^8 yr ago; c) the surface of 2003 EL61 is depleted of carbon chains. According to the orbital parameters of this population, this makes it a possible source of carbon-depleted Jupiter family comets.
About 20% of stars in the solar vicinity are in the Hercules stream, a bundle of stars that move together with a velocity distinct from the Sun. Its origin is still uncertain. Here, we explore the possibility that Hercules is made of trojans, stars captured at L4, one the Lagrangian points of the stellar bar. Using GALAKOS--a high-resolution N-body simulation of the Galactic disk--we follow the motions of stars in the co-rotating frame of the bar and confirm previous studies on Hercules being formed by stars in co-rotation resonance with the bar. Unlike previous work, we demonstrate that the retrograde nature of trojan orbits causes the asymmetry in the radial velocity distribution, typical of Hercules in the solar vicinity. We show that trojans remain at capture for only a finite amount of time, before escaping L4 without being captured again. We anticipate that in the kinematic plane the Hercules stream will de-populate along the bar major axis and be visible at azimuthal angles behind the solar vicinity with a peak towards L4. This test can exclude the OLR origin of the Hercules stream and be validated by Gaia DR3 and DR4.
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