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Nuno Peixinho - One of the best experts on this subject based on the ideXlab platform.

  • Low phase angle effects in photometry of Trans-Neptunian Objects: 20000 Varuna and 19308 (1996 TO66)
    Icarus, 2006
    Co-Authors: Irina N. Belskaya, J. L. Ortiz, Philippe Rousselot, V. Ivanova, G. Borisov, Vasilij G. Shevchenko, Nuno Peixinho
    Abstract:

    Abstract We present the results of photometric observations of Trans-Neptunian Object 20000 Varuna, which were obtained during 7 nights in November 2004–February 2005. The analysis of new and available photometric observations of Varuna reveals a pronounced opposition surge at phase angles less than 0.1 deg with amplitude of 0.2 mag relatively to the extrapolation of the linear part of magnitude–phase dependence to zero phase angle. The opposition surge of Varuna is markedly different from that of dark asteroids while quite typical for moderate albedo Solar System bodies. We find an indication of variations of the scattering properties over Varuna's surface that could result in an increase of the lightcurve amplitude toward zero phase angle. It is shown that a similar phase effect can be responsible for lightcurve changes found for TNO 19308 (1996 TO 66 ) in 1997–1999.

  • Coordinated thermal and optical observations of Trans-Neptunian Object (20 000)Varuna from Sierra Nevada
    Astronomy and Astrophysics, 2002
    Co-Authors: Emmanuel Lellouch, J. L. Ortiz, Raphael Moreno, Gabriel Paubert, A. Doressoundiram, Nuno Peixinho
    Abstract:

    We report on coordinated thermal and optical measurements of Trans-Neptunian Object (20000)Varuna obtained in January-February 2002, respectively from the IRAM 30-m and IAA 1.5 m telescopes. The optical data show a lightcurve with a period of 3.176 ′ 0.010 hr, a mean V magnitude of 20.37 ′ 0.08 and a 0.42 ′ 0.01 magnitude amplitude. They also tentatively indicate that the lightcurve is asymmetric and double-peaked. The thermal observations indicate a 1.12 ′ 0.41 mJy flux, averaged over the Object's rotation. Combining the two datasets, we infer that Varuna has a mean 1060 + 1 8 0 - 2 2 0 km diameter and a mean 0.038 + 0 . 0 2 2 - 0 . 0 1 0 V geometric albedo, in general agreement with an earlier determination using the same technique.

J. L. Ortiz - One of the best experts on this subject based on the ideXlab platform.

  • Discovery of a Satellite of the Large Trans-Neptunian Object (225088) 2007 OR10
    The Astrophysical Journal, 2017
    Co-Authors: Csaba Kiss, Gábor Marton, Anikó Farkas-takács, John Stansberry, Thomas Müller, József Vinkó, Zoltan Balog, J. L. Ortiz
    Abstract:

    2007 OR10 is currently the third largest known dwarf planet in the Trans-Neptunian region, with an effective radiometric diameter of ~1535 km. It has a slow rotation period of ~45 hr that was suspected to be caused by tidal interactions with a satellite undetected at that time. Here, we report on the discovery of a likely moon of 2007 OR10, identified on archival Hubble Space Telescope WFC3/UVIS system images. Although the satellite is detected at two epochs, this does not allow an unambiguous determination of the orbit and the orbital period. A feasible 1.5–5.8 1021 kg estimate for the system mass leads to a likely 35–100 day orbital period. The moon is about 42 fainter than 2007 OR10 in HST images that corresponds to a diameter of 237 km assuming equal albedos with the primary. Due to the relatively small size of the moon, the previous size and albedo estimates for the primary remains unchanged. With this discovery all Trans-Neptunian Objects larger than 1000 km are now known to harbor satellites, an important constraint for moon formation theories in the young solar system.

  • A mid-term astrometric and photometric study of Trans-Neptunian Object (90482) Orcus
    Astronomy and Astrophysics, 2010
    Co-Authors: J. L. Ortiz, A. Cikota, S. Cikota, Daniel Hestroffer, Audrey Thirouin, Nicolás Morales, René Duffard, R. Gil-hutton, Pablo Santos-sanz, I. De La Cueva
    Abstract:

    From time series CCD observations of a fixed and large star field that contained the binary Trans-Neptunian Object (90482) Orcus (formerly 2004 DW), taken during a period of 33 days, we have been able to derive high-precision relative astrometry and photometry of the Orcus system with respect to background stars. The right ascension residuals of an orbital fit to the astrometric data revealed a periodicity of 9.7 ± 0.3 days, which is what one would expect to be induced by the known Orcus companion (Vanth). The residuals are also correlated with the theoretical positions of the satellite with regard to the primary. We therefore have revealed the presence of Orcus’ satellite in our astrometric measurements, although the residuals in declination did not show the expected variations. The oscillation in the residuals is caused by the photocenter motion of the combined Orcus plus satellite system around the barycenter along an orbital revolution of the satellite. The photocenter motion is much larger than the motion of Orcus around the barycenter, and we show here that detecting some binaries through a carefully devised astrometric technique might be feasible with telescopes of moderate size. We discuss the prospects for using the technique to find new binary Trans-Neptunian Objects (TNOs) and to study already known binary systems with uncertain orbital periods. We also analyzed the system’s mid-term photometry in order to determine whether the rotation could be tidally locked to the satellite’s orbital period. We found that a photometric variability of 9.7 ±  0.3 days is clear in our data, and is nearly coincident with the orbital period of the satellite. We believe this variability might be induced by the satellite’s rotation. In our photometry there is also a slight hint for an additional very small variability in the 10 h range that was already reported in the literature. This short-term variability would indicate that the primary is not tidally locked and therefore the system would not have reached a double synchronous state. Implications for the basic physical properties of the primary and its satellite are discussed. From angular momentum considerations we suspect that the Orcus satellite might have formed from a rotational fission. This requires that the mass of the satellite would be around 0.09 times that of the primary, close to the value that one derives by using an albedo of 0.12 for the satellite and assuming equal densities for both the primary and secondary.

  • Low phase angle effects in photometry of Trans-Neptunian Objects: 20000 Varuna and 19308 (1996 TO66)
    Icarus, 2006
    Co-Authors: Irina N. Belskaya, J. L. Ortiz, Philippe Rousselot, V. Ivanova, G. Borisov, Vasilij G. Shevchenko, Nuno Peixinho
    Abstract:

    Abstract We present the results of photometric observations of Trans-Neptunian Object 20000 Varuna, which were obtained during 7 nights in November 2004–February 2005. The analysis of new and available photometric observations of Varuna reveals a pronounced opposition surge at phase angles less than 0.1 deg with amplitude of 0.2 mag relatively to the extrapolation of the linear part of magnitude–phase dependence to zero phase angle. The opposition surge of Varuna is markedly different from that of dark asteroids while quite typical for moderate albedo Solar System bodies. We find an indication of variations of the scattering properties over Varuna's surface that could result in an increase of the lightcurve amplitude toward zero phase angle. It is shown that a similar phase effect can be responsible for lightcurve changes found for TNO 19308 (1996 TO 66 ) in 1997–1999.

  • A study of Trans-Neptunian Object 55636 (2002 TX300)
    Astronomy and Astrophysics, 2004
    Co-Authors: J. L. Ortiz, P. J. Gutiérrez, Alfredo Sota, Raphael Moreno, Emmanuel Lellouch, N. Biver, Alain Doressoundiram, Philippe Rousselot, Isabel Márquez, R. M. González Delgado
    Abstract:

    We report on physical properties of the bright Trans-Neptunian Object 2003 TX300 based on a large set of observa- tions taken in different wavelength ranges. Broad band CCD observations aimed at studying the short-term rotational variability show a low amplitude periodic signal of 7.89 ± 0.03 h. We cannot yet determine whether the lightcurve is single-peaked (i.e. the rotation period would be 7.89 h) or double-peaked (i.e. the actual spin period would be 15.78 h). From a sinusoidal fit, the peak to peak amplitude of the brightness changes is 0.09 ± 0.08 mag. If the brightness changes are due to irregular shape, this amplitude implies a minimum axial ratio of 1.09. BVRI photometry indicates similar colors as other large Kuiper Belt members, with B − V = 0.64 ± 0.04, V − R = 0.40 ± 0.07, and R − I = 0.22 ± 0.05. Thermal observations at 250 GHz (1.2 mm) result in no confident detection of the body, with a measured flux of 0.22 ± 0.51 mJy. Combining all the data and using the same thermophysical model as in Lellouch et al. (2002) we find (at a 3-σ confidence level) a lower limit for the geometric albedo (pv > 0.06) and an upper limit for the size of this Object (D 0.08, which is significantly higher than the typical 0.04 cometary value and also higher than that of Varuna.

  • Rotational brightness variations in Trans-Neptunian Object 50000 Quaoar
    Astronomy and Astrophysics, 2003
    Co-Authors: J. L. Ortiz, P. J. Gutiérrez, Alfredo Sota, V. Casanova, V. R. Teixeira
    Abstract:

    Time-resolved broad-band CCD photometry of Trans-Neptunian Object 50000 Quaoar carried out using the 1.5 m telescope at Sierra Nevada Observatory is presented. The lightcurve reveals short-term variability due to rotation of the body. The periodogram analysis shows a peak at 8.8394 ± 0.0002 h with a confidence level above 99.9%. The lightcurve seems to be double-peaked, and therefore the rotation period would be 17.6788 ± 0.0004 h. The amplitude of the oscillation is 0.133 ± 0.028 mag. Under the assumption that the rotational variation is induced by an irregular shape, the minimum axial ratio of Quaoar would then be 1.133 ± 0.028.

Scott S. Sheppard - One of the best experts on this subject based on the ideXlab platform.

  • Physical Properties of Trans-Neptunian Object (20000) Varuna
    The Astronomical Journal, 2002
    Co-Authors: David Jewitt, Scott S. Sheppard
    Abstract:

    We present new time-resolved photometric observations of the bright Trans-Neptunian Object (20000) Varuna and use them to study the rotation period, shape, and color. In observations from 2001 February and April, we find a best-fit two-peaked light curve with period 6.3442 ± 0.0002 hr. The peak-to-peak photometric range in the R band is 0.42 ± 0.02 mag. We find no rotational variation in colors over the 0.45 μm ≤ λ ≤ 0.85 μm wavelength range. From the short, double-peaked period and large amplitude, we suggest that Varuna is an elongated, body, perhaps close in shape to one of the Jacobi ellipsoids. If so, the ratio of the axes projected into the plane of the sky is 1.5:1 and the density is near 1000 kg m-3. Varuna may be a rotationally distorted rubble pile, with a weak internal constitution due to fracturing by past impacts. The high specific angular momentum implied by our observations and recent detections of binary Trans-Neptunian Objects both point to an early, intense collisional epoch in which large Trans-Neptunian Objects were ~100 times more abundant than now. In order to maintain a cosmochemically plausible rock : ice mass ratio of ~0.5, Varuna must be internally porous.

David Jewitt - One of the best experts on this subject based on the ideXlab platform.

  • Physical Properties of Trans-Neptunian Object (20000) Varuna
    The Astronomical Journal, 2002
    Co-Authors: David Jewitt, Scott S. Sheppard
    Abstract:

    We present new time-resolved photometric observations of the bright Trans-Neptunian Object (20000) Varuna and use them to study the rotation period, shape, and color. In observations from 2001 February and April, we find a best-fit two-peaked light curve with period 6.3442 ± 0.0002 hr. The peak-to-peak photometric range in the R band is 0.42 ± 0.02 mag. We find no rotational variation in colors over the 0.45 μm ≤ λ ≤ 0.85 μm wavelength range. From the short, double-peaked period and large amplitude, we suggest that Varuna is an elongated, body, perhaps close in shape to one of the Jacobi ellipsoids. If so, the ratio of the axes projected into the plane of the sky is 1.5:1 and the density is near 1000 kg m-3. Varuna may be a rotationally distorted rubble pile, with a weak internal constitution due to fracturing by past impacts. The high specific angular momentum implied by our observations and recent detections of binary Trans-Neptunian Objects both point to an early, intense collisional epoch in which large Trans-Neptunian Objects were ~100 times more abundant than now. In order to maintain a cosmochemically plausible rock : ice mass ratio of ~0.5, Varuna must be internally porous.

Hsiang-kuang Chang - One of the best experts on this subject based on the ideXlab platform.

  • Search for serendipitous Trans-Neptunian Object occultation in X-rays
    Monthly Notices of the Royal Astronomical Society, 2012
    Co-Authors: Hsiang-kuang Chang, Kuan-ting Chen
    Abstract:

    To study the population properties of small, remote Objects beyond Neptune's orbit in the outer solar system, of kilometer size or smaller, serendipitous occultation search is so far the only way. For hectometer-sized Trans-Neptunian Objects (TNOs), optical shadows actually disappear because of diffraction. Observations at shorter wave lengths are needed. Here we report the effort of TNO occultation search in X-rays using RXTE/PCA data of Sco X-1 taken from June 2007 to October 2011. No definite TNO occultation events were found in the 334 ks data. We investigate the detection efficiency dependence on the TNO size to better define the sensible size range of our approach and suggest upper limits to the TNO size distribution in the size range from 30 m to 300 m. A list of X-ray sources suitable for future larger facilities to observe is proposed.

  • Millisecond dips in the RXTE/PCA light curve of Sco X-1 and Trans-Neptunian Object occultation
    Monthly Notices of the Royal Astronomical Society, 2007
    Co-Authors: Hsiang-kuang Chang, Jau-shian Liang, S. K. King
    Abstract:

    Millisecond dips in the RXTE/Proportional Counter Array (PCA) light curve of Sco X-1 were reported recently, which were interpreted as the occultation of X-rays from Sco X-1 caused by Trans-Neptunian Objects (TNO) of 100-m size. Inconclusive signatures of possible instrumental effects in many of these dip events related to high-energy cosmic rays were later found and the TNO interpretation became shaky. Here, we report more detailed analysis aiming at distinguishing true occultation events from those related to cosmic rays. Based on some indicative criteria derived from housekeeping data and two-channel spectral information, we suggest that about 10 per cent of the dips are probable events of occultation. The total number of TNOs of size from 60 to 100 m is estimated to be about 10 15 accordingly. Limited by the