Atomic Iron and Nickel in the Coma of C/1996 B2 (Hyakutake): Production Rates, Emission Mechanisms, and Possible Parents

Two papers recently reported the detection of gaseous nickel and iron in the comae of over 20 comets from observations collected over two decades, including interstellar comet 2I/Borisov. To evaluate the state of the laboratory data in support of these identifications, we reanalyzed archived spectra of comet C/1996 B2 (Hyakutake), one of the nearest and brightest comets of the past century, using a combined experimental and computational approach. We developed a new, many-level fluorescence model that indicates that the fluorescence emissions of Fe I and Ni I vary greatly with heliocentric velocity. Combining this model with laboratory spectra of an Fe-Ni plasma, we identified 22 lines of Fe I and 14 lines of Ni I in the spectrum of Hyakutake. Using Haser models, we estimate the nickel and iron production rates as Q Ni = (2.6–4.1) × 1022 s−1 and Q Fe = (0.4–2.8) × 1023 s−1. From derived column densities, the Ni/Fe abundance ratio log10[Ni/Fe] = −0.15 ± 0.07 deviates significantly from solar abundance ratios, and it is consistent with the ratios observed in solar system comets. Possible production and emission mechanisms are analyzed in the context of existing laboratory measurements. Based on the observed spatial distributions, excellent fluorescence model agreement, and Ni/Fe ratio, our findings support an origin consisting of a short-lived unknown parent followed by fluorescence emission. Our models suggest that the strong heliocentric velocity dependence of the fluorescence efficiencies can provide a meaningful test of the physical process responsible for the Fe I and Ni I emission.

On the role of collisions with meteoroids in splitting and acceleration of heliocentric velocity of comets

The hypothesis on the role of the meteoroid impacts in the comet nuclei splitting as well as acceleration of their heliocentric velocity are considered. Inclinations of the orbits of split comets relative to the movement planes of 100 known meteoroid streams are calculated. The analysis is carried out for the cases: when the cometary nodes are located from the meteoroids orbit < 0.1 AU; MOID-values less than 0.1 AU. In the case of split long-period comets irregularity (maximum near 180°) of the distribution of the inclinations has been found. Comets, constituting this maximum, could have head-on collisions with meteoroids. A similar analysis is carried out relatively to the hyperbolic comets (HCs). Analysis is based on the assumption that the acceleration of the heliocentric velocities of the comet also is caused by collisions with meteoroids. The inclinations of the orbits of 300 HCs relative to 100 known meteoroid streams have the significant maxima in the interval of 90°− 101.5°. Acceleration of comet velocity might be the result of “slanting” collisions with meteoroids.

KKH 22, the first dwarf spheroidal satellite of IC 342

Aims. We present observations with the Advanced Camera for Surveys on the Hubble Space Telescope of the nearby dwarf spheroidal galaxy KKH 22 = LEDA 2807114 in the vicinity of the massive spiral galaxy IC 342. Methods. We derived its distance of 3.12 ± 0.19 Mpc using the tip of red giant branch (TRGB) method. We also used the 6 m BTA spectroscopy to measure a heliocentric radial velocity of the globular cluster in KKH 22 to be +30 ± 10 km s−1. Results. The dSph galaxy KKH 22 has the V-band absolute magnitude of –12.m19 and the central surface brightness μv, 0 = 24.1m/□″. Both the velocity and the distance of KKH 22 are consistent with the dSph galaxy being gravitationally bound to IC 342. Another nearby dIr galaxy, KKH 34, with a low heliocentric velocity of +106 km s−1 has the TRGB distance of 7.28 ± 0.36 Mpc residing in the background with respect to the IC 342 group. KKH 34 has a surprisingly high negative peculiar velocity of –236 ± 26 km s−1.

The occurence of interstellar meteoroids in the vicinity of the Earth

If interstellar meteors are present among the registered meteor orbits, the distribution of the excesses of their heliocentric velocities should correspond to the distribution of radial velocities of close stars. Hence, for the velocity vi = 20 kms−1 of an interstellar meteor (with respect to the Sun) we obtain a heliocentric velocity vH = 46.6 kms−1 of an interstellar meteor arriving at the Earth. Moreover, a concentration of radiants to the Sun's apex should be observed. An analysis of the hyperbolic meteors among the 4581 photographic orbits of the IAU Meteor Data Center showed that the identification of the vast majority of the hyperbolic orbits in these catalogues has been caused by an erroneous determination of their heliocentric velocity and/or other parameters. Any error in the determination of vH, especially near the parabolic limit, can create an artificial hyperbolic orbit that does not really exist. On the basis of photographic meteors from the IAU MDC, the proportion of possible interstellar meteors decreased significantly (greater than 1 order of magnitude) after error analysis and does not exceed the value 2.5 × 10−4. Neither any concentration of radiants to the Sun's apex, nor any distribution following the motion of interstellar material has been found.

HI Study of the NGC 6744 System

We present the preliminary results of our 5-configuration, 20-pointing mosaic with the Australia Telescope Compact Array of the neutral hydrogen in the nearby spiral galaxy NGC 6744. The bulk of the HI resides in a ‘ring’ underlying the outer optical disk, with 2 HI spiral arms extending further out to almost 1·5 optical radii. The velocity field is fairly regular, apart from evidence for streaming motions along the HI arms, and the influence of the companion IB(s)m galaxy NGC 6744A. We associate a cloud of HI at a heliocentric velocity of 846 km s−1 with another companion object, ESO 104–g44. Our attempts to construct a mass model for NGC 6744 suffer from poor resolution in the inner disk, and the uncertainty in the total HI flux of NGC 6744. We anticipate that HIPASS observations will be crucial in resolving the latter issue.

10.8. A massive black hole in the active galaxy NGC6251

NGC 6251 is an E2 galaxy with mB = 13.6 mag (RC3) and heliocentric velocity 7400 km s−1(=106 Mpc for H0 = 70 km s−1Mpc−1). It is the host galaxy of one of the largest known radio sources in the sky: the radio lobes extend for 1°.2 (over 2 Mpc, Waggett et al. 1977, Readhead et al. 1978, Cohen and Readhead 1979, Jones et al. 1986, Jones and Wehrle 1994).

Low-Power Radio Sources in the Nuclei of Nearby E/S0 Galaxies: Evidence for Active Nuclei and for Current Star Formation

Galaxies were selected from the CfA redshift survey (Huchra et al. 1983, Ap.J.Suppl., 52, 189; Tonry 1984, private communication) according to: Decl.(1950) ≥ 0°; photographic or B(0) magnitude ≤ 14 mag; heliocentric velocity ≤ 3000 km s−1; and de Vaucouleurs morphological type T ≤ −1. The third criterion roughly corresponds to a distance limit of 40 Mpc for H0 = 75 km s−1 Mpc−1. The fourth criterion is equivalent to a Hubble morphological type of elliptical (E) or lenticular (S0), collectively referred to as E/S0 galaxies hereafter. 213 galaxies satisfy the above selection criteria, after 3 Local Group dwarf spheroidals are excluded. Various galaxy catalogs and the recent literature were consulted to check the CfA morphological classifications and to divide the galaxies into Es and S0s. These galaxies comprise a volume– and optical–magnitude–limited sample that is ideally suited to systematic searches in all spectral domains for low-power nuclear activity (Wrobel 1988, A.J., in press).

Velocity Dispersion and Luminosity Function of Planetary Nebulae in the Nuclear Bulge of M31

We used a sequence of velocity-modulated photographs to find and measure the radial velocities of faint planetary nebulae in the center of M31. The photographs were made with a Velocity Modulating Camera (VMC) which consists of a temperature-tuned 2.1 Å (FWHM) (O III) λ 5007 interference filter, a cooled, two-stage image intensifier, and a calibrating photomultiplier. The camera was mounted at the Cassegrain focus of the Shane 3 m telescope at Lick Observatory. We identified 19 new planetary nebulae, bringing the total number of known planetaries within 250 pc of M31's nucleus to 45. From the plate series, we derived radial velocities and relative brightnesses from 32 of the nebulae and placed radial velocity limits on the remaining nebulae in the field. By applying the method of maximum likelihood to the observed radial velocity distribution, we derive a mean heliocentric velocity of −309 (±25) km s−1 and a velocity dispersion of 155 (±22) km s−1 for the planetary nebulae.