Near-infrared spectra of 12 Near-Earth Objects

We present a number of spectra of Near-Earth Objects taken in the period 1998-2003 with two different instruments (CGS4 and UIST) on the UKIRT telescope. Since observations with CGS4 require multiple spectral fragments to be observed sequentially and then spliced together we assess the reliability of this technique using comparisons between multiple observations of the same object, between observations of the same object with both instruments and with independent spectra of common objects. We conclude that while problems in the spectral splicing can occur, they are usually intuitively obvious and that overall our dataset is sound. The objects for which we present new spectral data are: 1627 Ivar, 4179 Toutatis, 5381 Sekhmet, (5587) 1990 SB, 6489 Golevka, (11405) 1999 CV₃, (14402) 1991 DB, 25143 Itokawa, (25330) 1999 KV₄, (52760) 1998 ML₁₄, (66391) 1999 KW₄, and (101955) 1999 RQ₃₆. Our results, together with albedo data from the literature, suggest carbonaceous compositions for 25330 and 101955. The available data for 14402 suggest it may belong to the relatively rare M class. Our analysis suggests an S or Sq classification for 52760 and a V classification for 5381 Sekhmet. For all remaining objects the UKIRT data are consistent with published spectral classifications. We find that only 3 of the 12 objects are not S/Q/V-class, which is roughly consistent with the results of Binzel et al. [Binzel, R.P., Rivkin, A.S., Stuart, J.S., Harris, A.W., Bus, S.J., Burbine, T.H., 2004. Icarus 170, 259-294]. Four spectra of Toutatis taken over a range of solar phase angles between 0.7°-81° and at intervals of several weeks are indistinguishable within the uncertainties and therefore do not reveal any evidence for phase reddening or surface variegation.     

Searching for water ice on 47171 1999 TC36, 1998 SG35, and 2000 QC243: ESO large program on TNOs and centaurs

Transneptunian objects and Centaurs are supposed to be among the most pristine bodies of the Solar System. To investigate their physical properties and their surface composition, an ESO large program at the Very Large Telescope was carried out. In this paper we present photometric and spectroscopic near-infrared data of two Centaurs (1998 SG35 and 2000 QC243) and one transneptunian object (47171 1999 TC36). For 47171 1999 TC36 and 1998 SG35 visible photometry is also presented. Models of the surface composition of these objects are presented and discussed. By including a small percentage of water ice in our geographical mixtures, we obtain a better agreement with the observations in the H and K bands.     

Physical survey of 24 Centaurs with visible photometry

We present optical observations of 24 Centaurs performed between 1998 and 2002 with the University of Hawaii 2.2-m telescope. This is the largest such Centaur survey to date. We report colors for all objects, and show that they cover a continuum with mean V–R color of 0.58±0.01 and standard deviation 0.15. The color distribution fits between those of the Kuiper Belt and the cometary nuclei, and seems consistent with the dynamical concept of the majority of Centaurs originating from the Kuiper Belt. We find no strong correlation between a Centaur's color and its orbital elements; there is at best a <3−σ correlation with semimajor axis, with redder Centaurs being farther from the Sun. We have calculated the phase-darkening slope parameters G for 5 Centaurs, 4 of which are reported for the first time. They range from −0.18 to 0.13. We have sufficient data to constrain the rotation periods of two Centaurs, 1999 UG₅ (which we reported earlier) and 1998 SG₃5. We performed a comparison of the surface brightness profiles of 10 apparently-inactive Centaurs with point sources. We found no coma around these 10 objects, including C/LINEAR (2000 B4), and generally the upper limits to the dust mass loss rates are below 0.05 kg s⁻¹.     

Nova Sagittarii 1998 (V4633 Sgr): a permanent superhump system or an asynchronous polar?

We report the results of observations of V4633 Sgr (Nova Sagittarii 1998) during     . Two photometric periodicities were present in the light curve during the three years of observations: a stable one at     , which is probably the orbital period of the underlying binary system; and a second one of lower coherence, approximately 2.5 per cent longer than the former. The latter periodicity may be a permanent superhump, or, alternatively, the spin period of the white dwarf in a nearly synchronous magnetic system. A third period, at     , corresponding to the beat between the two periods was probably present in 1999. Our results suggest that a process of mass transfer has taken place in the binary system since no later than two-and-a-half months after the nova eruption. We derive an interstellar reddening of     from our spectroscopic measurements and published photometric data, and estimate a distance of     to this nova.     

Optical and infrared colors of transneptunian objects observed with HST

We present optical colors of 72 transneptunian objects (TNOs), and infrared colors of 80 TNOs obtained with the WFPC2 and NICMOS instruments, respectively, on the Hubble Space Telescope (HST). Both optical and infrared colors are available for 32 objects that overlap between the datasets. This dataset adds an especially uniform, consistent and large contribution to the overall sample of colors, particularly in the infrared. The range of our measured colors is consistent with other colors reported in the literature at both optical and infrared wavelengths. We find generally good agreement for objects measured by both us and others; 88.1% have better than 2 sigma agreement. The median absolute magnitude, H_V, magnitude of our optical sample is 7.2, modestly smaller (∼0.5 mag) than for previous samples. The median H_V in our infrared sample is 6.7. We find no new correlations between color and dynamical properties (semi-major axis, eccentricity, inclination and perihelion). We do find that colors of Classical objects with i < 6° come from a different distribution than either the Resonant or excited populations in the visible at the >99.99% level with a K-S test. The same conclusion is found in the infrared at a slightly lower significance level, 99.72%. Two Haumea collision fragments with strong near infrared ice bands are easily identified with broad HST infrared filters and point to an efficient search strategy for identifying more such objects. We find evidence for variability in (19255) 1999 VK₈, 1999 OE₄, 2000 CE₁₀₅, 1998 KG₆₂ and 1998 WX₃₁.     

Merging Massive Star Clusters as Building Blocks of Dwarf Galaxies?

Recent spectroscopic observations of galaxies in the Fornax-Cluster reveal nearly unresolved ‘star-like’ objects with red-shifts appropriate to the Fornax-Cluster. These objects have intrinsic sizes of ≈ 100 pc and absolute B-band magnitudes in the range - 14 < M_B < -11.5 mag and lower limits for the central surface brightness μ_B ≥ 23 mag/arcsec² (Phillipps et al., 2001, Hilker et al., 1999), and so appear to constitute a new population of ultra-compact dwarf galaxies (UCDs). Such compact dwarfs were predicted to form from the amalgamation of stellar super-clusters (= clusters of star clusters; not to confuse with super stellar clusters (SSC)) by P. Kroupa (1998), which are rich aggregates of young massive star clusters (YMCs) that can form in collisions between gas-rich galaxies. Here we present the evolution of super-clusters in a tidal field. The YMCs merge on a few super-cluster crossing times. Super-clusters that are initially as concentrated and massive as Knot S in the interacting Antennae galaxies (Whitmore et al., 1999) evolve to merger objects that are long-lived and show properties comparable to the newly discovered UCDs. This revised version was published online in September 2006 with corrections to the Cover Date.     

A survey of orbits of co-orbitals of Mars

Many asteroids with a semimajor axis close to that of Mars have been discovered in the last several years. Potentially some of these could be in 1:1 resonance with Mars, much as are the classic Trojan asteroids with Jupiter, and its lesser-known horseshoe companions with Earth. In the 1990s, two Trojan companions of Mars, 5261 Eureka and 1998 VF₃₁, were discovered, librating about the L₅ Lagrange point, 60° behind Mars in its orbit. Although several other potential Mars Trojans have been identified, our orbital calculations show only one other known asteroid, 1999 UJ₇, to be a Trojan, associated with the L₄ Lagrange point, 60° ahead of Mars in its orbit. We further find that asteroid 36017 (1999 ND₄₃) is a horseshoe librator, alternating with periods of Trojan motion. This asteroid makes repeated close approaches to Earth and has a chaotic orbit whose behavior can be confidently predicted for less than 3000 years. We identify two objects, 2001 HW₁₅ and 2000 TG₂, within the resonant region capable of undergoing what we designate “circulation transition”, in which objects can pass between circulation outside the orbit of Mars and circulation inside it, or vice versa. The eccentricity of the orbit of Mars appears to play an important role in circulation transition and in horseshoe motion. Based on the orbits and on spectroscopic data, the Trojan asteroids of Mars may be primordial bodies, while some co-orbital bodies may be in a temporary state of motion.     

Asteroid identification using BTA images

We report the results of identification of the Main Belt asteroid 2006 HO 153 accidentally found during the observations of transneptunian objects in 1998. We briefly describe the technique of identification, where the use of change rates of spherical coordinates of the observed asteroid plays an important role.     

The scattered trans-Neptunian object 1998 XY95

On 1998 December 12 a new trans-Neptunian object, 1998 XY95, was discovered as part of a deep search. Recent observations of this object have placed it amongst the class of objects known as the scattered trans-Neptunian objects (TNOs). A total of 39 CCD images of 1998 XY95 were taken over two nights, and these were used to search for a light curve, but no significant periodicity was found. An examination of the possible orbital evolution gives no indication of how it may have arrived on its present orbit. The current best-fitting orbit is unstable, but remains within a band of semi-major axis approximately 2 au wide. The bottom of this band is due to 3:1 mean motion resonance with Neptune, while the reason for the top of the band remains unclear.     

New Variable Stars Discovered as By-product of the Beijing Astronomical Observatory Supernova Survey

The Beijing Astronomical Observatory (BAO) 0.6 m telescope has been used for nearby supernova survey in more than 3000 fields, covering a total area of 235 deg2. More than 260000 CCD images have been collected since April 1996, with 45 supernovae discovered. We searched for variables in about 90000 images taken during 1996-1998. For the fields in which long period variables (LPVs) were discovered, we reduced further images taken from 1999 to 2000, for the period estimation. Among the 280000 stars selected from the survey fields, i.e., brighter than 18 mag, we discovered seven new LPVs and reconfirmed three known LPVs. Additionally, we found 146 variable star candidates, and reconfirmed about 20 previously known or suspected objects.     

大气492 GHz亚毫米波不透明度的测量

使用移动式亚毫米波望远镜(POST)在位于青藏高原海拔3200米的紫金山天文台德令哈射电天文观测站址测量地球大气492GHz频率处天顶方向的不透明度(τ0)的结果．在1999—2000年冬季和2000—2001年冬季的两个观测季节内累计共进行了约870个小时的测量，取得了25842组τ0的有效数据．对数据的统计表明，观测季节内τ0值主要分布在1．5—3．0之间．观测时段内大气不透明度τ0≤1．0的时间比例约占3％．在给出实测资料的基础上，将所测量的亚毫米波不透明度与国际现有亚毫米波台址的不透明度进行了初步比较．     

Spectroscopic observations of Jupiter Trojans

We present the results of a campaign of spectroscopic observations of Jupiter Trojan asteroids. Thirty-four objects were observed during three runs in July and November 1998, and March 2002 using the Danish 1.54-m telescope at ESO. The covered spectral range was between 5000 and 9000 Å. Our observations include objects belonging both L₄ to L₅ clouds. According to analyses of previous investigations of Trojans, the spectra of different taxonomic classes can be separated on the basis of the slope of the reflectance spectrum. The large majority of the objects of our sample have been found to belong to the D taxonomic class, but we found also objects of P- and C-type. In two cases, we found also evidence of blueish spectral trends. Our data are important, since they allow us to substantially enlarge the whole data set of available Trojan spectra.     

O3 Profiles from GOME satellite data—II: Observations in the Arctic Spring 1997 and 1998

Ozone observations by the Global Ozone Monitoring Experiment (GOME) on board the ERS-2 satellite during the Arctic spring periods 1997 and 1998 are presented. From the derived ozone vertical distributions, extensive regions of low ozone total column were observed and it is shown that the major decrease is dominating in the lower and middle stratosphere inside the polar vortex. The winter 1997/98 was warmer than the year before and less ozone depletion was observed. In spring 1998 an ozone mini-hole event was observed by GOME and ozone profiles under minihole conditions were derived for the first time.     

A radar survey of main-belt asteroids: Arecibo observations of 55 objects during 1999-2003

We report Arecibo observations of 55 main-belt asteroids (MBAs) during 1999-2003. Most of our targets had not been detected previously with radar, so these observations more than double the number of radar-detected MBAs. Our bandwidth estimates constrain our targets' pole directions in a manner that is geometrically distinct from optically derived constraints. We present detailed statistical analyses of the disk-integrated properties (radar albedo and circular polarization ratio) of the 84 MBAs observed with radar through March 2003; all of these observations are summarized in the online supplementary information. Certain conclusions reached in previous studies are strengthened: M asteroids have higher mean radar albedos and a wider range of albedos than do other MBAs, suggesting that both metal-rich and metal-poor M-class objects exist; and C- and S-class MBAs have indistinguishable radar albedo distributions, suggesting that most S-class objects are chondritic. Also in accord with earlier results, there is evidence that primitive asteroids from outside the C taxon (F, G, P, and D) are not as radar-bright as C and S objects, but a convincing statistical test must await larger sample sizes. In contrast with earlier work, we find S-class MBAs to have higher circular polarization ratios than other MBAs, indicating greater near-surface structural complexity at decimeter scales, due to different mineralogy (material strength or loss tangent), a different impactor population, or both.     

Late-type stars found in the FBS. New carbon stars

We present new observations of seven late-type stars previously discovered in the First Byurakan Survey (FBS). These observations prove that they belong to the family of carbon (C) stars. Seventy-nine similar FBS C stars were previously known. The seven objects under analysis were presented in the FBS lists as M or C star candidates. Among the seven objects, six objects are confirmed by low-resolution spectra of the Hamburg Quasar Objective-Prism Survey. We also present for five of them moderate-resolution spectra obtained at optical wavelengths with a spectrograph equipped with a CCD detector. Three objects can be classified as N-type C stars. One object is an early CH-type C star. Most likely, the star FBS 1339+117 belongs to the group of carbon dwarfs. We estimate distances of these seven new C stars either by using their red-band magnitudes, or by using their near-infrared 2MASS J-K_S color and K_S-band magnitudes. Published in Astrofizika, Vol. 51, No. 2, pp. 255–265 (May 2008).     

Studies of bright flat-spectrum radio quasar 3C 454.3 at high and very-high-energies

Blazars are the subclass of active galactic nuclei (AGNs) which includes the Flat Spectrum Radio Quasars (FSRQ) and BL Lacertae (BL Lac) objects. Variability on the short- and long-time scale in all the wide energy ranges from radio up to gamma-ray emission is a special characteristic of blazars. Multi-wavelength studies of the flaring activity and variability of blazars can serve as a tool to probe the physical properties of the near the core regions and processes responsible for the observed features. 3C 454.3 is a bright FSRQ that is intensively studied through the wide range of electromagnetic spectrum. It has shown remarkably high activity since 2000. The long-term observations of 3C 454.3 at 800 GeV–100 TeV energies with the SHALON telescope were started in 1998 year. A number of activity periods were found. The most significant flaring state of 3C 454.3 at TeV energies was detected in the SHALON observational period of November–December 2010. This increase is correlated with the flares at a lower energy range in observations of Fermi-LAT. The direct association of the significant changes of gamma-ray flux with strong core radio flares are not clear but observed correlations and lags in multi-wavelength activity may point to the complexity of the emission processes in blazars connected with disturbance propagating in the jet.     

Hawaii Kuiper Belt Variability Project: An Update

We have been systematically monitoring a large sample of bright Kuiper Beltobjects for possible light variations due to rotational and phase angle effects.Here we report on three objects, 2003 AZ₈₄, (24835) 1995 SM₅₅and (55636) 2002 TX₃₀₀ observed to have measurable rotational lightcurveswith peak-to-peak amplitudes of 0.14 ± 0.03, 0.19 ± 0.05 and 0.08 ± 0.02magnitudes and single-peaked periods of 6.71 ± 0.05, 4.04 ± 0.03 and8.12 ± 0.08 hours, respectively. We observed a further ten objects whichshowed no rotational photometric variation within measurement uncertainties.In addition, we find that the lightcurve of 1995 SM₅₅ may have a variableamplitude. We discuss this peculiar object as well as our observations of the reportedlyvariable Kuiper Belt object (19308) 1996 TO₆₆. Finally, we continue to find the phase functions of the Kuiper Belt objects to be very steep and linear, to firstorder, with a median slope of 0.16 ± 0.01 magnitudes per degree in the phaseangle range 0 to 2 degrees.     

Surface composition and physical properties of several trans-neptunian objects from the Hapke scattering theory and Shkuratov model

Several different trans-neptunian objects have been studied in order to investigate their physical and chemical properties. New observations in the 1.1-1.4 μm range, obtained with the ISAAC instrument, are presented in order to complete previous observations carried out with FORS1 in the visible and SINFONI in the near infrared. All of the observations have been performed at the ESO/Very Large Telescope. We analyze the spectra of six different objects (2003 AZ₈₃, Echeclus, Ixion, 2002 AW₁₉₇, 1999 DE₉ and 2003 FY₁₂₈) in the 0.45-2.3 μm range with the model of Hapke (Hapke, B. [1981]. J. Geophys. Res. 86, 4571-4586) and the method of Shkuratov et al. (Shkuratov, Y., Starukhina, L., Hoffmann, H., Arnold, G. [1999]. Icarus 137, 235-246). Water ice is found on two objects, and in particular it is confirmed in its amorphous and crystalline states on 2003 AZ₈₄ surface. Upper limits on the water ice content are given for the other four TNOs investigated, confirming previous results (Barkume, K.M., Brown, M.E., Schaller, E.L. [2008]. Astron. J. 135, 55-67; Guilbert, A., Alvarez-Candal, A., Merlin, F., Barucci, M.A., Dumas, C., de Bergh, C., Delsanti, A. [2009]. Icarus 201, 272-283). Whatever the absorption features in the near infrared, all objects but one exhibit a moderate red slope in the visible, as most TNOs and Centaurs. We discuss the implications of the presence of water ice and the probable sources of the red slope.     

Preparing for the 1998/99 Leonid Storms

In order to further observing programs aimed at the possible meteor storms of November 1998 and 1999, we describe here how the Leonid shower is expected to manifest itself on the sky. We discuss: 1) the expected wavelength dependence of meteor (train) emission, 2) the meteor brightness distribution and influx, 3) the stream cross section, radiant and altitude of the meteors, 4) the apparent fluxes at various positions in the sky as a function of radiant elevation as well as 5) the trail length and radial velocity, and 6) the diameter and brightness of persistent trains as a function of radiant elevation. These topics were chosen to help researchers plan an observing strategy for imaging, spectroscopy, and LIDAR observations. Some applications are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Near-infrared sky background fluctuations at mid- and low latitudes

The emission of the upper atmosphere introduces an additional variable component into observations of astronomical objects in the NIR 700–3,000 nm range. The subtraction of this component is not easy because it varies during the night by as much as 100% and it is not homogeneous over the sky. A program aimed at measuring and understanding the main characteristics of the atmospheric NIR emission was undertaken. A 512?×?512 CCD camera equipped with a RG780/2 mm filter is used to obtain images of the sky in a 36°?×?36° field of view. The intensities of a given star and of the nearby region devoid of star in a 439 arcmin² area are monitored during periods of time of several hours. The sky intensity measured in the 754–900 nm bandpass, reduced to zenith and zero airmass is comprised between mag20 and mag18.5 per arcsecond². A diminution by a factor of two during the night is frequently observed. Intensity fluctuations having an amplitude of 15% and periods of 5–40 min are present in the images with a structure of regularly spaced stripes. The fluctuations of the NIR sky background intensity are due to (1) the chemical evolution of the upper atmosphere composition during the night and (2) dynamical processes such as tides with periods of 3–6 h or gravity waves with periods of several tens of minutes. We suggest that a monitoring of the sky background intensity could be set up when quantitative observations of astronomical objects require exposure times longer than ~10 min. The publication is illustrated with several video films accessible on the web site http://www.obs-besancon.fr/nirsky/. Enter username: nirsky and password: skynir.