Visible spectroscopy of the new ESO large programme on trans-Neptunian objects and Centaurs: final results

Abstract

Context.A second large programme (LP) for the physical studies of TNOs and Centaurs, started at ESO Cerro Paranal on October 2006 to obtain high-quality data, has recently been concluded. In this paper we present the spectra of these pristine bodies obtained in the visible range during the last two semesters (November 2007−November 2008) of the LP. Aims. We investigate the spectral behaviour of the TNOs and Centaurs observed, and we analyse the spectral slopes distribution of the full data set coming from this LP and from the literature. Methods. Spectroscopic observations in the visible range were carried out at the UT1 (Antu) telescope using the instrument FORS2. We computed the spectral slope for each observed object, and searched for possible weak absorption features. A statistical analysis was performed on a total sample of 73 TNOs and Centaurs to look for possible correlations between dynamical classes, orbital parameters, and spectral gradient. Results. We obtained new spectra for 28 bodies (10 Centaurs, 6 classical, 5 resonant, 5 scattered disk, and 2 detached objects), 15 of which were observed for the first time. All the new presented spectra are featureless, including 2003 AZ84, for which a faint and broad absorption band possibly attributed to hydrated silicates on its surface has been reported. The data confirm a wide variety of spectral behaviours, with neutral-grey to very red gradients. An analysis of the spectral slopes available from this LP and in the literature for a total sample of 73 Centaurs and TNOs shows that there is a lack of very red objects in the classical population. We present the results of the statistical analysis of the spectral slope distribution versus orbital parameters. In particular, we confirm a strong anticorrelation between spectral slope and orbital inclination for the classical population. Nevertheless, we do not observe a change in the slope distribution at i ∼ 5 • , the boundary between the dynamically hot and cold populations, but we find that objects with i < 12 • show no correlation between spectral slope and inclination, as has already been noticed on the colour-inclination relation for classical TNOs. A strong correlation is also found between the spectral slope and orbital eccentricity for resonant TNOs, with objects having higher spectral slope values with increasing eccentricity.

The extra red plutino (55638) 2002 VE95

“…Barucci et al (2006) already observed it spectroscopically and detected water ice and clear evidence of methanol in its surface. Fornasier et al (2009) (90377) Sedna, and different from the previous visible observations reported by Barucci et al (2006), for which the computed slope was 27.9 ± 0.1%/(10 3 Å). The period is not well known, Ortiz et al (2006) reported a noisy lightcurve with a small amplitude of about 0.08 with possible periodicities of 6.76 or 9.47 hrs.…”

“…Using the new constraints of the albedo value, we model the complete set of new available spectra as well the previous published data A&A 539, A152 (2012) Fornasier et al (2009). to investigate the surface composition properties and search for surface variation.…”

Taxonomy of trans-Neptunian objects and Centaurs as seen from spectroscopy

“…Part of the data have been published for this object. Photometry in both wavelength ranges has been presented in Perna et al (2010) while results based on visible spectroscopy have been presented in Fornasier et al (2009) Table 1. Seventeen exposures of 600 s were taken in a jitter pattern, for a total exposure time of 2 h 50 min.…”

Methane, ammonia, and their irradiation products at the surface of an intermediate-size KBO?

“…Near-infrared photometry from Gemini+NIRI (this work) and near-infrared published colors from Orcus. Fornasier et al (2009). The three top spectra were shifted by 0.5 in reflectance for clarity.…”

“…6), we draw a similar conclusion for the case of Orcus. (208996) (208996) has a quasi-neutral featureless spectrum in the optical, with a spectral slope of 1.6 ± 0.6%/100 nm (Fornasier et al 2009, and references therein). Guilbert et al (2009) confirmed the presence of water ice (Barkume et al 2008) in its crystalline phase from near-infrared spectroscopy, and noted a possible absorption feature around 2.3 μm.…”