arXiv subjects

Michał Drahus

Publications and source records attributed to Michał Drahus.

3 recordsLinked to original sources

arXiv2021

Gaseous atomic nickel in the coma of interstellar comet 2I/Borisov

On 31 August 2019, an interstellar comet was discovered as it passed through the Solar System (2I/Borisov). Based on initial imaging observations, 2I/Borisov appeared to be completely similar to ordinary Solar System comets - an unexpected characteristic after the multiple peculiarities of the only previous known interstellar visitor 1I/'Oumuamua. Spectroscopic investigations of 2I/Borisov identified the familiar cometary emissions from CN, C2, O I, NH2, OH, HCN, and CO, revealing a composition similar to that of carbon monoxide-rich Solar System comets. At temperatures >700 K, comets additionally show metallic vapors produced by the sublimation of metal-rich dust grains. However, due to the high temperature needed, observation of gaseous metals has been limited to bright sunskirting and sungrazing comets and giant star-plunging exocomets. Here we report spectroscopic detection of atomic nickel vapor in the cold coma of 2I/Borisov observed at a heliocentric distance of 2.322 au - equivalent to an equilibrium temperature of 180 K. Nickel in 2I/Borisov seems to originate from a short-lived nickelbearing molecule with a lifetime of $340^{+260}_{-200}$ s at 1 au and is produced at a rate of $0.9 \pm 0.3 \times 10^{22}$ atoms s$^{-1}$, or 0.002% relative to OH and 0.3% relative to CN. The detection of gas-phase nickel in the coma of 2I/Borisov is in line with the concurrent identification of this atom (as well as iron) in the cold comae of Solar System comets.

astro-ph.EP↗

arXiv2019

Initial characterization of interstellar comet 2I/Borisov

Interstellar comets penetrating through the Solar System had been anticipated for decades. The discovery of asteroidal-looking 'Oumuamua was thus a huge surprise and a puzzle. Furthermore, the physical properties of the 'first scout' turned out to be impossible to reconcile with Solar System objects, challenging our view of interstellar minor bodies. Here, we report the identification and early characterization of a new interstellar object, which has an evidently cometary appearance. The body was discovered by Gennady Borisov on 30 August 2019 UT and subsequently identified as hyperbolic by our data mining code in publicly available astrometric data. The initial orbital solution implies a very high hyperbolic excess speed of ~32 km/s, consistent with 'Oumuamua and theoretical predictions. Images taken on 10 and 13 September 2019 UT with the William Herschel Telescope and Gemini North Telescope show an extended coma and a faint, broad tail. We measure a slightly reddish colour with a g'-r' colour index of 0.66 +/- 0.01 mag, compatible with Solar System comets. The observed morphology is also unremarkable and best explained by dust with a power-law size-distribution index of -3.7 +/- 1.8 and a low ejection speed (44 +/- 14 m/s for $β$ = 1 particles, where $β$ is the ratio of the solar gravitational attraction to the solar radiation pressure). The nucleus is probably ~1 km in radius, again a common value among Solar System comets, and has a negligible chance of experiencing rotational disruption. Based on these early characteristics, and putting its hyperbolic orbit aside, 2I/Borisov appears indistinguishable from the native Solar System comets.

astro-ph.EP↗

arXiv2018

The Excited Spin State of 1I/2017 U1 `Oumuamua

We show that `Oumuamua's excited spin could be in a high energy LAM state, which implies that its shape could be far from the highly elongated shape found in previous studies. CLEAN and ANOVA algorithms are used to analyze `Oumuamua's lightcurve using 818 observations over 29.3~days. Two fundamental periodicities are found at frequencies (2.77$\pm$0.11) and (6.42$\pm$0.18)~cycles/day, corresponding to (8.67$\pm$0.34)~h and (3.74$\pm$0.11)~h, respectively. The phased data show that the lightcurve does not repeat in a simple manner, but approximately shows a double minimum at 2.77~cycles/day and a single minimum at 6.42~cycles/day. This is characteristic of an excited spin state. `Oumuamua could be spinning in either the long (LAM) or short (SAM) axis mode. For both, the long axis precesses around the total angular momentum vector with an average period of (8.67$\pm$0.34)~h. For the three LAMs we have found, the possible rotation periods around the long axis are 6.58, 13.15, or 54.48~h, with 54.48~h being the most likely. `Oumuamua may also be nutating with respective periods of half of these values. We have also found two possible SAM states where `Oumuamua oscillates around the long axis with possible periods at 13.15 and 54.48~h, the latter as the most likely. In this case any nutation will occur with the same periods. Determination of the spin state, the amplitude of the nutation, the direction of the TAMV, and the average total spin period may be possible with a direct model fit to the lightcurve. We find that `Oumuamua is "cigar-shaped"', if close to its lowest rotational energy, and an extremely oblate spheroid if close to its highest energy state for its total angular momentum.

astro-ph.EP↗