Simultaneous visible and near-infrared time resolved observations of the outer solar system object (29981) 1999 TD 10

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1 Simultaneous visible and near-infrared time resolved observations of the outer solar system object (29981) 1999 TD 10 Béatrice E. A. Mueller National Optical Astronomy Observatory 1, 950 N Cherry Ave, Tucson AZ muller@noao.edu Carl W. Hergenrother Lunar and Planetary Laboratory, University of Arizona, Tucson AZ Nalin H. Samarasinha National Optical Astronomy Observatory 1, 950 N Cherry Ave, Tucson AZ Humberto Campins University of Central Florida, Orlando FL and Lunar and Planetary Laboratory, University of Arizona, Tucson AZ Donald W. McCarthy, Jr. Steward Observatory, University of Arizona, Tucson AZ Accepted by Icarus, June 17, The National Optical Astronomy Observatory is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. 1

2 ABSTRACT The outer solar system object (29981) 1999 TD 10 was observed simultaneously in the R, and J and H bands in September 2001, and in B, V, R, and I in October We derive B-V=0.80±0.05 mag, V-R=0.48±0.05 mag, R-I=0.44±0.05 mag, R-J=1.24±0.05 mag, and J-H=0.61±0.07 mag. Combining our data with the data from Rousselot et al. (Astron. Astrophys. 407, 1139, 2003) we derive a synodic period of ±0.001 hr in agreement with the period from Rousselot et al. Our observations at the same time, with better S/N and seeing, show no evidence of a coma, contrary to the claim by Choi et al. (Icarus 165, 101, 2003). Key Words: Asteroids, rotation; Centaurs; Photometry; Infrared Observations; (29981) 1999 TD 10 2

3 I. INTRODUCTION The outer solar system object (29981) 1999 TD 10, referred to hereafter as TD 10,was discovered by the Spacewatch survey (Scotti et al. 1999). It has a perihelion distance of 12 AU, similar to Centaurs and an aphelion distance of 190 AU characteristic of many scattered disk objects. Consolmagno et al. (2000), assuming an albedo of 0.04, estimate the object s major and minor axes as 130 and 70 km respectively (i.e. an effective radius of 50 km). This indicates a large outer solar system object with an irregular shape. They find a periodicity in the lightcurve of 5.8 hr (which corresponds to a single peaked lightcurve) and a gray color. Rousselot et al. (2003) derive a solar phase dependence in the H-G scattering formalism and a period of ±0.002 hr. Choi et al. (2003) report a period of ±0.012 hr and derive a solar phase dependence and an effective radius of 58 km. They also claim to have detected a coma in TD 10. We compare our results with the literature above and investigate the claim of coma activity. In section II we describe our visible and near-infrared observations and reductions, in section III, we discuss the photometry, the lightcurve and the colors of TD 10. In section IV we consider and reject the claim of coma activity, and we summarize our results in section V. II. OBSERVATIONS AND REDUCTIONS TD 10 was observed simultaneously in the visible and near-infrared from September UT, 2001, with two additional nights in the visible on September 23 and 25, It was also observed about one year later in the visible from October 30 November 1, The summary of the observational and the geometrical circumstances are given in Table I. Table I Observational and Geometric Circumstances for TD 10 Date Filters r a b α c sky condition [UT] [AU] [AU] [deg] 09/21/01 R,J photometric 09/22/01 R,J,H photometric 09/23/01 R photometric 09/25/01 R photometric 10/30/02 B,V,R,I photometric 10/31/02 R photometric 11/01/02 R not photometric a heliocentric distance b geocentric distance c solar phase angle 3

4 A. Visible data The visible observations in both runs were taken with the KPNO-2.1m telescope on Kitt Peak equipped with a Tektronix CCD chip with 24 µm pixels. At a focal ratio of f/7.5, the plate scale is pix 1 and the field of view is Standard Harris broad-band filters which are optimized for the Kron-Cousins system were used. The integration time was limited as not to smear out the rotational signature. The trailing rates corresponded to less than half the seeing disk. Standard IRAF procedures were used to reduce the data. The images were bias subtracted and then flat fielded with combined dome flats to remove the pixel to pixel variations. Dithered object frames were combined with a rejection criteria to remove the objects and smoothed to correct for the difference in slope between the dome flats and the dark sky. In addition, fringe correction frames were constructed from combined object frames in the I-band to remove the fringing. The resulting reduced images were flat to better than 1%. Relative photometry was carried out with at least 6 comparison stars in the same frame to extract the magnitude of TD 10. An aperture diameter of 14 pix (4. 3) which was always at least twice as large as the maximum seeing was used for the photometry of the object and an aperture diameter of 30 pix (9. 2) was used for the comparison and standard stars. The aperture correction to tie the object to the comparison stars was done for every frame separately. There were common stars in frames of subsequent nights, so that the nights could be tied to a reference night. There were at least two photometric nights per observing run (Table I) and the absolute calibration was done using Landolt Standard Star fields (Landolt 1992). B. Near-infrared data The near-infrared observations were obtained with the University of Arizona s Steward Observatory 2.3m Bok telescope on Kitt Peak with the PISCES infrared camera. PISCES consists of a 1024x1024 Rockwell Hawaii detector with 18.5 µm pixels (Mc- Carthy et al. 2001). The PISCES camera has a final focal ratio of f/3.3 and a plate scale of pix 1 at the 2.3m Bok telescope. Standard IRAF procedures were employed to reduce the data. Images were dark subtracted and flat fielded with median sky flats produced from the individual dithered J and H-band images. A routine was used to remove the effect of cross-talk between CCD readout quadrants (McCarthy et al. 2001). Absolute photometry in J (λ c =1.25 µm) and H (λ c =1.65 µm) was determined from observations of standards P309-U, P533-D and S677-D (Persson et al. 1998) at multiple airmasses. Variations in seeing did not allow for the use of a single aperture for photometry. The standards were measured with an aperture diameter of 6 FWHM which ranged from 8 to 16 pixels (4 to 8 ). TD 10 was measured with an aperture diameter of 2 FWHM. An aperture correction was determined and used to normalize the photometry. Both nights were photometric allowing absolute calibrations. The solar colors in the Arizona infrared photometric system (Campins et al. 1985) were 4

5 used for conversion from fluxes to reflectances (section III.D). III. Photometry A. Lightcurve Analysis The magnitudes R(1,1,α), i.e. the observed R magnitude corrected to heliocentric and geocentric distances of 1 AU each, but not corrected for solar phase angle effects are given in Table II for September 2001 and in Table III for October The times in both Tables are light time corrected and refer to the midpoint of the integrations. Figure 1 shows the R-band data from September 23, 2001 and from October 30, In September 2001 we observed a maximum but no minima and in October 2002 we observed a minimum and a maximum. The peak to peak variation in the lightcurve is 0.50 mag. This variation is consistent with the peak to peak variation of 0.68 mag given by Consolmagno et al. (2000). As the geometry was different for our observations compared to that of Consolmagno et al. (2000) and their lightcurve amplitude is larger than ours, our observations must have been taken when the rotational angular momentum vector was closer to the line of sight. The J data for September 21 and 22, 2001 are given in Table IV and the H data for September 22, 2001 are given in Table V. The times in both Tables are again light time corrected and refer to the midpoints of the integrations. The lightcurve for the J data from September 21, 2001 is shown in Figure 2. B. Solar phase dependence Before doing a periodicity analysis, our data will have to be corrected first for changes in heliocentric and geocentric distances and phase angle. The solar phase dependence of TD 10 is not known. We did not adopt the phase dependence of Choi et al. (2003) because our derived mean absolute magnitudes using their solar phase coefficient for the September 2001 and October 2002 data do not agree with each other. Their derivation is also widely different from the range of linear solar phase coefficients for 7 TNOs by Sheppard and Jewitt (2002). The derived phase coefficient of β=0.121 mag deg 1 by Rousselot et al. (2003) is in agreement with the mean solar phase coefficient by Sheppard and Jewitt (2002). However, our mean absolute magnitudes in September 2001 and October 2002 using this coefficient are still inconsistent with each other. This could be due to the different nuclear orientations caused by the observing geometries, but the difference in geocentric (or heliocentric) ecliptic longitude of TD 10 between these two dates is only 10 and in ecliptic latitude is 1. We used the maxima in the R-band lightcurve from September 23, 2001 and from November 1, 2002 to derive the solar phase angle dependence. We get for the absolute mean magnitude R 0 =8.43±0.01 mag, and for the solar phase coefficient β=0.181±0.015 mag deg 1. As the two maxima in a double peaked lightcurve do not have to be equal, we derived the solar phase coefficient by comparing the mean magnitudes for the September 2001 and October 2002 run. We get the same coefficient as that 5

6 Table II R-band photometry for TD 10 in September 2001 JD a R(1,1,α) error JD a R(1,1,α) error a light time corrected, at midpoint of integration 6

7 Table III R-band photometry for TD 10 in October 2002 JD a R(1,1,α) error JD a R(1,1,α) error a light time corrected, at midpoint of integration 7

8 Figure 1: Visible lightcurve in R from September 23, 2001 (top) and from October 30, 2002 (bottom). 8

9 Table IV J-band photometry for TD 10 in September 2001 JD a J(1,1,α) error JD a J(1,1,α) error

10 Table IVcontinued JD a J(1,1,α) error JD a J(1,1,α) error a light time corrected, at midpoint of integration 10

11 Table V H-band photometry for TD 10 in September 2001 JD a H(1,1,α) error JD a J(1,1,α) error a light time corrected, at midpoint of integration derived from comparing the maxima. This is not surprising since, as the phase plot in Figure 7 shows, the two maxima in the lightcurve are indeed equal in magnitude. This solar phase coefficient is inside the range of coefficients quoted by Sheppard and Jewitt (2002). The derivation of the solar phase coefficient is dependent on the accuracy of the absolute calibration of the data. We had two photometric nights each in both observing runs and the difference in absolute magnitude within a run is mag in September 2001 and mag in October If we assume a maximum difference in absolute magnitudes of mag between the two runs, then the corresponding change in the derived solar phase coefficient β is mag deg 1 which is of the same order as the error of β quoted above. R 0 is consistent with R opp derived by Choi et al. (2003) and H R by Rousselot et al. (2003). C. Period Analysis In order to identify as well as to minimize artifacts, we used two different techniques for the period search analysis of the R-band lightcurves: fitting harmonics and using a Fourier Transform (FT) with a subsequent WindowCLEAN algorithm (Belton and Gandhi 1988, Mueller et al. 2002). The clean spectrum is a deconvolution of the FT of the observed data (dirty spectrum) with the spectral window. The spectral window (or dirty beam) is the FT of the sampling function which is 0 when no observation was 11

12 Figure 2: Near-infrared lightcurve in J from September 21,

13 taken and 1 when an observation was taken. The χ 2 plot of fitting the harmonics and the dirty and clean power spectra for the WindowCLEAN for the individual data sets from September 2001 and October 2002 are shown in Figure 3. The minimum for September 2001 in the χ 2 plot is at a frequency f of 3.13 dy 1. The maximum in the clean power spectrum is at 3.11 dy 1. Taking the standard deviations of the power spectrum signatures and the χ 2 signatures as the maximum of the error, we obtain 0.12 dy 1 for the error. The two frequencies are in excellent agreement with each other. Assuming that the lightcurve is due to an aspherical shape, the corresponding double peaked periods (P = 2 ) are 15.34±0.3 hr and 15.43±0.3 hr. f For October 2002, the frequencies derived are 3.12 dy 1 from the χ 2 plot and 3.14 dy 1 from the clean spectrum, again in good agreement with each other. The corresponding periods are 15.38±0.3 hr from fitting harmonics and 15.29±0.3 hr from WindowCLEAN. The minor adjacent peaks to the maximum peak in the dirty spectra for the 2001 and 2002 data are likely daily aliases. This is confirmed as the phase plots with their corresponding periods are unacceptable. The periods derived from our 2001 and 2002 data sets seem to be in conflict with the single peak period of 5.8 hr quoted by Consolmagno et al. (2000). The corresponding frequency of the double peaked equivalent is 4.14 dy 1, which is the same as one of our minor peaks in the dirty spectrum and is a daily alias. They did not do a detailed period analysis and their data fit well with any of our periods quoted above (priv. comm. by S. C. Tegler, 2003). The simultaneous near-infrared data agree well with the period derived from the R-band data. We can derive a very accurate period by combining the September 2001 and October 2002 data because of the large time baseline of over one year. We applied the FT and WindowCLEAN as well as fitting harmonics to the combined data set from September 2001 and October 2002 (Figure 4). Two frequencies at ± dy 1 and at ± dy 1 are left by the WindowCLEAN. Both of these frequencies are also present in the χ 2 plot. The double peaked period corresponding to the first frequency does not give a satisfactory phase plot and is rejected. The second frequency gives a double peaked period of ±0.001 hr. As the gap between the two data sets is about a year, the results of the Window- CLEAN algorithm need to be checked. The maximum peaks in the dirty spectrum area at frequencies dy 1 and dy 1. However, phase plots with the corresponding periods are not acceptable. We then checked all the peaks from the dirty spectrum between frequencies of 3.11 dy 1 and 3.14 dy 1. This is the frequency range derived from the September 2001 and October 2002 data separately. Although, some of the corresponding periods give unacceptable results, some give phase plots that are as good as the one with the period of hr. We also applied WindowCLEAN to the combined data sets with slightly different solar phase corrections. The dirty spectra were the same within the errors. The WindowCLEAN picked the adjacent peaks to the one corresponding to the hr period. We do not have enough temporal coverage 13

14 Figure 3: χ 2 plot (top), and dirty (middle) and clean (bottom) power spectra for the R-band data from September 2001 on the left and for October 2002 on the right. 14

15 Figure 4: χ 2 plot (top), and dirty (middle) and clean (bottom) power spectra for the R-band data from September 2001 and October 2002 combined. The resolution of the x-axis increases from left to right. 15

16 in this case for WindowCLEAN to break all the aliases. The error in the period due to synodic effects has to be estimated. The time difference between the maxima in October 2002 and September 2001 corresponds to 634 cycles. The difference in geometry is roughly 10 between September 2001 and P[sec] 10 October 2002 (see above). This gives a change in period of the order of ( ) resulting in a synodic effect of less than hr. A phase plot of our data with the period from Rousselot et al. (2003) is acceptable. A phase plot with the period from Choi et al. (2003) does not fit our data at all. We checked the dirty spectra from our combined data sets and the data set of Rousselot et al. (2003) for frequency peaks close to the frequency corresponding to the period derived by Choi et al. (2003). The frequencies found were different but inside the error bars from the frequency from Choi et al. (2003). None of the corresponding periods resulted in phase plots that fit our data or the Rousselot et al. (2003) data. We applied the same WindowCLEAN algorithm to the data of Rousselot et al. (2003) and get two peaks, one at 3.120±0.004 dy 1 (P=15.385±0.009 hr) and the other at 3.138±0.004 dy 1 (P=15.296±0.009 hr) in order of falling power. The first peak is the same that Rousselot et al. (2003) derive from their data and the second one is one of the acceptable periods from our combined 2001 and 2002 data. We then combined our data set with the data set from Rousselot et al. (2003) and obtain a peak at ± dy 1 (P=15.382±0.001 hr) from the clean spectrum. The same frequency is present in the χ 2 plot as well. The corresponding χ 2 -plot and the dirty and clean spectra are shown in Figure 5. Because of the large gap in our combined data sets, caution has to be exercised in accepting the result from the WindowCLEAN algorithm without further checks. We used the dirty spectra from the Rousselot et al. (2003) data alone, our September 2001 and October 2002 data combined, as well as our data sets combined with the Rousselot et al. (2003) data, to compare the dirty spectra in the relevant frequency range. There were three common peaks. The peaks from the data of Rousselot et al. (2003) are: dy 1, dy 1, and dy 1. The standard deviation for all three peaks is dy 1. From our combined 2001 and 2002 data sets they are: dy 1, dy 1, and dy 1. The standard deviation for all three peaks is dy 1. From our data set combined with the Rousselot et al. (2003) data they are: dy 1, dy 1, and dy 1. The standard deviation is again dy 1. The comparison of the dirty spectra is shown in Figure 6. Although the corresponding peaks are inside the error bars, phase plots of the data from Rousselot et al. (2003) with periods from our peaks do not fit except for the peak at dy 1. The same is true for using the periods from the peaks from the Rousselot et al. (2003) data for our data set. We conclude that the peak at dy 1 is the only one consistent with all three dirty spectra. A phase plot with all the data for a period of hr is given in Figure 7. The spread and small systematic differences in the phase plot between our data and the data from Rousselot et al. (2003) can be attributed to the uncertain solar phase dependence corrections. 16

17 Figure 5: χ 2 plot (top), and dirty (middle) and clean (bottom) power spectra for our R-band data combined with the Rousselot et al. (2003) data. The resolution of the x-axis increases from left to right. 17

18 Figure 6: Comparison of the dirty spectra in the frequency range from 3.09 dy 1 to 3.15 dy 1. The top panel shows the dirty spectrum from the Rousselot et al. (2003) data alone, the middle panel from our September 2001 and October 2002 data combined, and the bottom panel shows the dirty spectrum from our combined data sets combined with the Rousselot et al. (2003) data. The marks on the peaks denote the 3 common peaks discussed in the text. 18

19 Figure 7: Phase plot of our R-band data from September 2001 (blue), October 2002 (green), and the data from Rousselot et al. (2003) (red) for a period of hr. 19

20 As Choi et al. (2003) did not publish their data in tabulated form, we cannot phase their data with the period of hr. However, in their figure 2, they give the location of their minimum and we can therfore deduce the locations of their maxima and compare those with the loaction of our maximum from September 2003 (see our figure 1). The locations of their maxima is consistent with our period of hr within the errors. D. Near-infrared and visible colors In addition to the lightcurve observations in R, we took observations in B, V, and I on October 30, Because of the good rotational phase coverage we can derive accurate colors unaffected by rotational effects. The average of four color observations in each of the above filters gives B-R=1.28±0.02 mag, V-R=0.48±0.05 mag, and R-I=0.44±0.05 mag. This gives B-V=0.80±0.05 mag. These colors are in excellent agreement with colors from the literature. A comparison of our colors and those from the literature are given in Table VI. The near-infrared data are noisier but have a higher time resolution than the visible data. We binned the J and H data in order to derive colors. We obtained simultaneous observations of J and R and of H and R. Comparing the R lightcurve with the J data and H data and comparing the rotationally phased data gives consistent results. We derive R-J=1.24±0.05 mag and R-H=1.85±0.05 mag, resulting in J-H=0.61±0.07 mag. With the above colors this results in V-J=1.72±0.08 mag. Our near-infrared colors and colors from the literature are again compared in Table VI. Table VI Comparison of visible and near-infrared colors for TD 10 Object B-V V-R R-I V-J J-H Reference a TD ± ± ± ± ±0.07 Mu TD ± ±0.02 R TD ± ± ±0.03 HD TD ± ±0.01 TR TD ±0.06 Mc Sun H Sun HTMC Sun CRL a Mu = this work, R = Rousselot et al. (2003), HD = Hainaut and Delsanti (2002), TR = Tegler and Romanishin (2003), Mc = McBride et al. (2003), H = Hardorp (1980), HTMC = Hartmann et al. (1990), CRL = Campins et al. (1985) The solar colors from Table VI were subtracted from the colors of TD 10. We then derived the relative reflectances of TD 10 which are normalized with respect to the R-band. They are shown in Figure 8. 20

21 Figure 8: Relative reflectance plot. The plot has been normalized with respect to the R-band. 21

22 We also converted our colors to the so called slope parameter or spectral index S [% (0.1 µm) 1 ] (Hainaut and Delsanti 2002) using S = 100 R(λ 2) R(λ 1 ) (λ 2 λ 1 with R the relative reflectivity and λ the central wavelength in µm. Following the approach of Hainaut )/0.1 and Delsanti (2002), we derived S for V, R, and I through linear regression. The result is S=7.5±3.1 % (0.1 µm) 1 compared with S=11.9±1.9 % (0.1 µm) 1 from Hainaut and Delsanti (2002). These values are within each other s error bars. Jewitt (2002) uses the V and R filters to derive the normalized reflectivity gradient S [% (0.1 µm) 1 ] from V-R=(V-R) +2.5log( 2+S λ ), with (V-R) 2 S λ as the solar color. For TD 10 we derive S =10.8±0.9 % (0.1 µm) 1. This value is close to the median S =10 % (0.1 µm) 1 for 9 Centaurs (Jewitt 2002). IV. ACTIVITY Choi et al. (2003) claim to have detected cometary activity in TD 10 on November 2 and 5, 2000 and on September 22, Our September data are bracketing their data from September 22. To investigate this claim in our data, we spatially shifted and combined all the images from September 21 23, 2001 to enhance the signal-to-noise for TD 10. The same procedure was applied to the stars in the field. The resulting effective integration time is 3.6 hr, a factor of 1.5 longer than that of Choi et al. (2003). We used a 2.1m telescope which gives a collection area 4.4 times larger than that from their 1m telescope. Additionally the seeing in our combined image is 1. 3 compared to their average seeing of No evidence of a resolved coma could be detected in our data, in agreement with the non-detection of a coma in the November 2002 data by Rousselot et al. (2003). As our September data bracket the data from Choi et al. (2003) on September 22, an intermittent coma can also be excluded. In Figure 9a the combined image centered on TD 10 is shown. No indication of a coma extension in any direction is seen. Figure 9b shows a comparison of the spatial profiles of TD 10 and a star in the same field with a similar flux, normalized to the same peak surface brightness. The error bars have been omitted for the star for clarity. There seem to be inconsistencies in the paper by Choi et al. (2003). The position angle of the antisolar direction is 252 for the September 2001 data and 66 for the November 2000 data, according to the JPL Horizons ephemeris. This leads to the conclusion that their coma extension is not in the antisolar direction contrary to their claim. In addition, the shape of this claimed coma extension is very unusual. The radial brightness profile for TD 10 dips below the profile of the comparison star and then rises back up to the previous level (see their Figure 6b). Also, the deviation of the profile of TD 10 from that of the comparison star starts after a distance from the center of the object at 5. At that distance the noise is dominant in our profile of TD 10 (see our Figure 9b), as well as in the profile from Rousselot et al. (2003) (see their Figure 2), both of which have better S/N than that from Choi et al. (2003). 22

23 Figure 9: a) Combined image of TD 10 from September 21 23, The figure is 30 (99 pixels) on the side. North is to the top and East is to the left. The antisolar direction is to the Southwest (PA=252 ). 23

24 Figure 9: b) Comparison of the spatial profiles of TD 10 and a comparison star from the combined images with a total integration time of 3.6 hr. 24

25 V. DISCUSSION AND SUMMARY TD 10 is a large outer solar system body with an irregular shape. Its visible colors are not unusual. Tegler et al. (2003) find a bimodal distribution for Centaurs in (B-R) for a sample of 22 Centaurs. Peixinho et al. (2003) also find a bimodal color distribution in (V-R) versus (B-V) for a sample of 20 Centaurs and they group the Centaurs into either blue (like 2060 Chiron) or red (like 5145 Pholus). The visible colors (Table VI) place TD 10 in the blue group (at the red end). There are only 7 Centaurs in common between the paper of Tegler et al. (2003) and Peixinho et al. (2003) and only one is outside each others error bars. On the other hand, Bauer et al. (2003) find a continuous color distribution for 24 Centaurs in their (V-R) versus (R-I) color-color plot. A direct comparison between the plots of Tegler and Romanishin (2003) and Peixinho et al. (2003) with those of Bauer et al. (2003) is not possible. Tegler et al. (2003) have 10 objects in common with Bauer et al. (2003) and only one is outside each others error bars. Peixinho et al. (2003) and Bauer et al. (2003) have 18 objects in common with 11 objects agreeing well, 2 objects having colors outside their error bars and 5 objects within each others combined error bars. If we take the V-R colors from Bauer et al. (2003) and the B-V colors from Peixinho et al. (2003), the gap in the (V-R) versus (B-V) plot vanishes. However, the error bars from the colors of Bauer et al. (2003) are generally larger than those from Peixinho et al. (2003). This emphasizes the need for careful extraction of colors. This includes taking into account effects of large amplitude variations in the lightcurves due to rotation. On the other hand, the difference in colors for some objects could be real due to large scale color variegations on the surface or due to temporal changes of the surface colors. As other authors noted, there seems to be a prevalence of large aspherical objects among the TNOs and Centaurs (e.g. Ortiz et al. 2003, Sheppard and Jewitt 2002). Approximately 8% of main belt asteroids with diameters larger than 90 km have axial ratios larger than 1.5. With the caveat of small number statistics (total number of objects is 27), the percentage of large (i.e. H V 7.5) TNOs and Centaurs with axial ratios larger than 1.5 is 22%. TD 10 was excluded from the statistic as its value of H V is larger than 7.5. What processes make main belt asteroids of this size more spherical on average than TNOs and Centaurs. Is this a selection effect or small statistics effect? Is it an inherent property of TNOs and Centaurs or an evolutionary effect? Sheppard and Jewitt (2002) note that the distribution of axial ratios of TNOs is not consistent with the distribution of impact fragment shapes. The knowledge of shapes and rotational periods of TNOs and Centaurs is clearly a very powerful tool in understanding the intrinsic and evolutionary properties of these objects. The summary of our results is listed below. The synodic period of TD 10 is ±0.001 hr assuming the lightcurve variation is due to an aspherical nucleus. No coma activity is detected. An intermittent coma can be excluded as well. We derive visible and near-infrared colors for TD 10 including its first J-H color. 25

26 The normalized reflectivity gradient is S =10.8±0.9 % (0.1 µm) 1, and is close to the median for Centaurs. ACKNOWLEDGMENTS It is a pleasure to thank Drs Michael J. S. Belton and Tod R. Lauer for help with acquiring the data. We are very grateful to Drs Stephen Tegler and Philippe Rousselot for providing their data in electronic form. This work was supported by Planetary Astronomy Grants from NASA for BEAM, NHS and HC, and by an NSF Grant for HC. REFERENCES Bauer, J.M., Meech, K.J., Fernández, Y.R., Pittichova, J., Hainaut, O.R., Boehnhardt, H., Delsanti, A.C Physical survey of 24 Centaurs with visible photometry. Icarus 166, Belton, M.J.S., Gandhi, A Application of the CLEAN algorithm to cometary light curves. Bull. Am. Astron. Soc. 20, 836 (abstract). Campins, H., Rieke, G.H., Lebofsky, M.J Absolute calibration of photometry at 1 through 5 microns. Astron. J. 90, Choi, Y.J., Brosch, N., Prialnik, D Rotation and cometary activity of KBO (29981) 1999 TD 10. Icarus 165, Consolmagno, G.J., Tegler, S.C., Rettig, T., Romanishin, W Size, shape, rotation, and color of the outer solar system object 1999 TD10. Bull. Am. Astron. Soc. 32, 1032 (abstract). Hainaut, O.R., Delsanti, A.C Colors of minor bodies in the outer solar system a statistical analysis. Astron. Astrophys. 389, Hardorp, J The Sun among stars. III. Energy distribution of 16 northern G-type stars and the solar flux calibration. Astron. Astrophys. 91, Hartmann, W.K., Tholen, D., Meech, K., Cruikshank, D Chiron: Colorimetry and cometary behavior. Icarus 83, Jewitt, D.C From Kuiper belt object to cometary nucleus: the missing ultrared matter. Astron. J. 123, Landolt, A.U UBVRI photometric standard stars in the magnitude range 11.5 <V <16.0 around the equator. Astron. J. 104,

27 McBride, N., Green, S.F., Davies, J.K., Tholen, D.J., Sheppard, S.S., Whitely, R.J., Hillier, J.K Visible and infrared photometry of Kuiper belt objects: searching for evidence of trends. Icarus 161, McCarthy, D.W., Ge, J., Hinz, J.L., Finn, R.A., de Jong, R.S PISCES: A wide-field, µm camera for large-aperture telescopes. Pub. Astron. Soc. Pac. 113, Mueller, B.E.A., Samarasinha, N.H., Belton, M.J.S The diagnosis of complex rotation in the lightcurve of 4179 Toutatis and potential applications to other asteroids and bare cometary nuclei. Icarus 158, Ortiz, J.L., Gutiérrez, P.J., Casanova, V., Sota, A A study of short term rotational variability in TNOs and Centaurs from Sierra Nevada observatory. Astron. Astrophys. 407, Peixinho, N., Doressoundiram, A., Delsanti, A., Boehnhardt, H., Barucci, M.A., Belskaya, I Reopening the TNO color controversy: Centaurs bimodality and TNOs unimodality. Astron. Astrophys. 410, L29-L32. Persson, S.E., Murphy, D.C., Krzeminski, W., Roth, M., Rieke, M.J A new system of faint near-infrared standard stars. Astron. J. 116, Rousselot, P., Petit, J-M., Poulet, F., Lacerda, P., Ortiz, J Photometry of the Kuiper-Belt object 1999 TD 10 at different phase angles. Astron. Astrophys. 407, Scotti, J.V., Larsen, J.A., May, B., Maggs, D TD10. M.P.E.C T46. Sheppard, S.S., Jewitt, D.C Time-resolved photometry of Kuiper belt objects: rotations, shapes, and phase functions. Astron. J. 124, Tegler, S.C., Romanishin, W Resolution of the Kuiper belt object color controversy: two distinct color populations. Icarus 161, Tegler, S.C., Romanishin, W., Consolmagno, G.J Color patterns in the Kuiper belt: a possible primordial origin. Astroph. J. 599, L49-L52. 27