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Publications - papers mentioned as co-author and/or collaborator


The Astrophysical Journal Letters, Volume 776, Number 2  - Karen J. Meech et al. 2013 ApJ 776 L20 doi:10.1088/2041-8205/776/2/L20


We report photometric observations for comet C/2012 S1 (ISON) obtained during the time period immediately after discovery (r = 6.28 AU) until it moved into solar conjunction in mid-2013 June using the UH2.2 m, and Gemini North 8 m telescopes on Mauna Kea, the Lowell 1.8 m in Flagstaff, the Calar Alto 1.2 m telescope in Spain, the VYSOS-5 telescopes on Mauna Loa Hawaii and data from the CARA network. Additional pre-discovery data from the Pan STARRS1 survey extends the light curve back to 2011 September 30 (r = 9.4 AU). The images showed a similar tail morphology due to small micron sized particles throughout 2013. Observations at submillimeter wavelengths using the James Clerk Maxwell Telescope on 15 nights between 2013 March 9 (r = 4.52 AU) and June 16 (r = 3.35 AU) were used to search for CO and HCN rotation lines. No gas was detected, with upper limits for CO ranging between 3.5-4.5 × 1027 molecules s–1. Combined with published water production rate estimates we have generated ice sublimation models consistent with the photometric light curve. The inbound light curve is likely controlled by sublimation of CO2. At these distances water is not a strong contributor to the outgassing. We also infer that there was a long slow outburst of activity beginning in late 2011 peaking in mid-2013 January (r ~ 5 AU) at which point the activity decreased again through 2013 June. We suggest that this outburst was driven by CO injecting large water ice grains into the coma. Observations as the comet came out of solar conjunction seem to confirm our models.

Comet McNaught (260P/2012 K2): spin axis orientation and rotation period          ( The final publication is available at


            Extensive observations of comet 260P/McNaught were carried out between August 2012 and January 2013. The images obtained were used to

Analyze the comet’s inner coma morphology at resolutions between 250 and 600 km/pixel.

A deep investigation of the features in the inner coma allowed us to identify only one main active source on the comet’s nucleus, at an

estimated latitude of -50° ± 10°. No other sources have been found in the images collected during the observing period.

Graphic simulations of the geometrical conditions of the observations were compared with the treated images to study the appearance and the

Possible motion of the morphological structures, and were used to determine a pole orientation at RA = 55° ± 10°, Dec = -15° ± 10°.

The comet's spin axis has never reached the plane of the sky from October 2012 to January 2013; during this period its direction did not change

More than 30°, thus giving us the opportunity to observe in the inner coma mainly structures such as bow-shaped jets departing from a single

active source located on the comet's nucleus.

During the months of August and September 2012 the polar axis was directed towards the Earth at an angle of about 50° from the plane of the

sky, and this has made it possible to observe the development of faint structures as fragments of shells or spirals.

A possible rotation period of 0.342 days has been estimated by means of differential photometric analysis.


The Astrophysical Journal Letters Volume 734 Number 1 - K. J. Meech et al. 2011 ApJ 734 L1 doi:10.1088/2041-8205/734/1/L1


Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P/Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period was ~16.4 hr. Starting in 2010 August the period changed from 16.6 hr to near 19 hr in December. With respect to dust composition, most volatiles and carbon and nitrogen isotope ratios, the comet is similar to other Jupiter-family comets. What is unusual is the dominance of CO2-driven activity near perihelion, which likely persists out to aphelion. Near perihelion the comet nucleus was surrounded by a large halo of water-ice grains that contributed significantly to the total water production.

Photometry and imaging of Comet 103P/Hartley in the 2010–2011 apparition

Icarus   -    Volume 222, Issue 2, February 2013, Pages 786–798   -    Stardust/EPOXI


The results of a CARA (Cometary Archive for Afρ) campaign on Comet 103P/Hartley 2 are presented. The main goal was to monitor extensively the

 comet during the apparition with CCD R and I imaging and photometry, as a support of EPOXI mission.

The Afρ quantity showed a progressively rising ascending branch, followed by an apparent flat maximum that lasted for 2 months, from about −10 to

+50 days from perihelion. In this period, Afρ peaked at around 100 cm in R band with strong short term fluctuations between 70 and 140 cm. Early

signs of activity were detectable well before perihelion (about 80–90 days before) and a random variability is also present in the descending branch

after perihelion. Three post perihelion data points (between +55 and +61 days) from the 1997–1998 apparition show a bit higher Afρ value of our

observation and a similar fast variation.

The average Afρ behavior, corrected for the solar phase effect, is strongly asymmetric and shows a more steeper ascending branch, approaching to


Morphology and coma asymmetry, as well as the sunward and tailward profiles are examined. An average gradient indicatively between +/- ρ−0.7 and

ρ−1 is observed in the inner coma (ρ < 2000 km). Ten small amplitude outbursts have been detected and two ones were suspected.


arXiv:1409.7641 [astro-ph.EP]  -  Submitted on 26 Sep 2014


Outbursts are known to begin with a sudden appearance and steep brightening of a "stellar nucleus" --- an unresolved image of a plume of material on its way from the comet's surface and an initial stage of an expanding halo of ejecta. Since the brightness of this feature is routinely reported, together with astrometry, by most comet observers as the "nuclear magnitude," it is straightforward to determine the onset time, a fundamental parameter of any outburst, by inspecting the chronological lists of such observations for a major jump in the nuclear brightness. Although it is inadmissible to mix nuclear magnitudes by different observers without first carefully examining their compatibility, the time constraints obtained from data sets reported by different observers can readily be combined. The intersection of these sets provides the tightest possible constraint on the outburst's onset time. Applied to comet 168P/Hergenrother during its 2012 return to perihelion, three outbursts were detected and their timing determined with good to excellent accuracy. Six fragmentation events experienced by the comet are shown to have occurred in the same period of time as the outbursts. Three companions are likely to have broken off from the primary in the first outburst, two companions in the second outburst, and one companion in the last outburst. All companions were short-lived, belonging to the class of excessively brittle fragments. Yet, the results suggest that most of the mass lost in the first outburst remained relatively intact during the liftoff, while the opposite was the case in the last outburst.

Photometry of Comet 9P/Tempel 1 during the 2004/2005 approach and the Deep Impact module impact

Icarus  -  Volume 187, Issue 1, March 2007, Pages 276–284   -   Deep Impact Mission to Comet 9P/Tempel 1, Part 1


The results of the 9P/Tempel 1 CARA (Cometary Archive for Amateur Astronomers) observing campaign is presented. The main goal was to perform an

extended survey of the comet as a support to the Deep Impact (DI) Mission. CCD R, I and narrowband aperture photometries were used to monitor the

Afρ quantity. The observed behavior showed a peak of 310 cm 83 days before perihelion, but we argue that it can be distorted by the phase effect, too.

The phase effect is roughly estimated around 0.0275 mag/degree, but we had no chance for direct determination because of the very similar geometry

of the observed apparitions. The log-slope of Afρ was around −0.5 between about 180–100 days before the impact but evolved near the steady-state

like 0 value by the impact time. The DI module impact caused about a 60% increase in the value of Afρ and a cloud feature in the coma profile which

was observed just after the event. The expansion of the ejecta cloud was consistent with a fountain model with initial projected velocity of 0.2 km/s and

β=0.73. Referring to a 25,000 km radius area centered on the nucleus, the total cross section of the ejected dust was View the MathML source 0.06 days

after the impact, and View the MathML source 1.93 days after the impact (A is the dust albedo). Five days after the event no signs of the impact were

detected, nor deviations from the expected activity referring both to the average pre-impact behavior and to the previous apparitions.

Herschel and IRAM-30m Observations of Comet C/2012 S1 (ISON) at 4.5 AU from the Sun

L. O'Rourke, D. Bockelée-Morvan, N. Biver, B. Altieri, D. Teyssier, L. Jorda, V. Debout, C. Snodgrass, M. Küppers, M. A'Hearn, T. G. Müller, T. Farnham

(Submitted on 25 Nov 2013)

    Our goal was to characterize the distant gaseous and dust activity of comet C\2012 S1 (ISON), inbound, from observations of H2O, CO and the dust coma in the far-infrared and submillimeter domains. In this paper, we report observations undertaken with the Herschel Space Observatory on 8 & 13 March 2013 (rh = 4.54 - 4.47AU) and with the 30m telescope of Institut de Radioastronomie Millim\'etrique (IRAM) in March and April 2013 (rh = 4.45 - 4.18 AU). The HIFI instrument aboard Herschel was used to observe the H2O 110−101 line at 557 GHz, whereas images of the dust coma at 70 and 160 {\mu}m were acquired with the PACS instrument. Spectra acquired at the IRAM 30m telescope cover the CO J(2-1) line at 230.5 GHz. The spectral observations were analysed with excitation and radiative transfer models. A model of dust thermal emission taking into account a range of dust sizes is used to analyse the PACS maps. While H2O was not detected in our 8 March 2013 observation, we derive a sensitive 3 σ upper limit of QH2O < 3.5 x 1026 molecules/s for this date. A marginal 3.2 σ detection of CO is found, corresponding to a CO production rate of QCO = 3.5 x 1027 molecules/s. The Herschel PACS measurements show a clear detection of the coma and tail in both the 70 {\mu}m and 160 {\mu}m maps. Under the assumption of a 2 km radius nucleus, we infer dust production rates in the range 10 - 13 kg/s or 40 - 70 kg/s depending on whether a low or high gaseous activity from the nucleus surface is assumed. We constrain the size distribution of the emitted dust by comparing PACS 70 and 160 {\mu}m data, and considering optical data. Size indices between -4 and -3.6 are suggested. The morphology of the tail observed on 70 {\mu}m images can be explained by the presence of grains with ages older than 60 days.

'Dust environment and dynamical history of a sample of short period comets'

F.J. Pozuelos,        F. Moreno,  F. Aceituno, V. Casanova,  A. Sota, J.J. Lopez-Moreno, J. Castellano, E. Reina, A.Diepvens, A. Betoret, B. Husler, C. Gonzlez, D. Rodrguez, E. Bryssinck, E. Corts, F. Garca, F. Garca, F.Limn, F. Grau, F. Fratev, F. Baldrs, F. A. Rodriguez, F. Montalbn, F. Soldn, G. Muler, I. Almendros, J.

Temprano, J. Bel, J. Snchez, J. Lopesino, J. Bez, J. F. Hernndez, J. L. Martn, J. M. Ruiz, J. R. Vidal, J. GaitnJ. L. Salto, J. M. Aymam, J. M. Bosch, J. A. Henrquez, J. J. Martn, J. Lacruz, L. Tremosa, L. Lahuerta, M.Reszelsky, M. Rodrguez, M. Camarasa, M. Campas, O. Canales, P.J. Dekelver, Q. Moreno, R. Benavides, R.Naves, R. Dymoc, R. Garca, S. Lahuerta, T. Climent  (submitter 2014 may 5th)



In this work, we present an extended study of the dust environment of a sample of short period comets and their dynamical

history. With this aim, we characterized the dust tails when the comets are active, and we made a statistical study to determine their

dynamical evolution. The targets selected were 22P/Kop, 30P/Reinmuth 1, 78P/Gehrels 2, 115P/Maury, 118P/Shoemaker-Levy 4,123P/West-Hartley, 157P/Tritton, 185/Petriew, and P/2011 W2 (Rinner).

Methods. We use two different observational data: a set of images taken at the Observatorio de Sierra Nevada and theAfp-curves provided by the amateur astronomical associationCometas-Obs

. To model these observations, we use our Monte Carlo dust tail code.

From this analysis, we derive the dust parameters, which best describe the dust environment: dust loss rates, ejection velocities, and

size distribution of particles. On the other hand, we use a numerical integrator to study the dynamical history of the comets, which

allows us to determine with a 90% of confidence level the time spent by these objects in the region of Jupiter Family Comets.


From the Monte Carlo dust tail code, we derived three categories attending to the amount of dust emitted: Weakly active

(115P, 157P, and Rinner), moderately active (30P, 123P, and 185P), and highly active (22P, 78P, and 118P). The dynamical studies

showed that the comets of this sample are young in the Jupiter Family region, where the youngest ones are 22P (100 yr), 78P (500yr), and 118P (

600 yr). The study points to a certain correlation between comet activity and time spent in the Jupiter Family region,although this trend is not always fulfilled. The largest particle sizes are not tightly constrained, so that the total dust mass derived should be regarded as lower limits.


Zdenek Sekanina - Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, U.S.A.


In early April 2017, five weeks before passing through perihelion, t he dust-poor comet C/2015 ER61 was observed to undergo a major outburst, during   which its intrinsic brightness increased briefly by about 2 mag. Evidence is presented in this paper to suggest that the flare-up was in all likelihood a product of an event of nuclear fragmentation that gave birth to a companion nucleus, which was first

detected more than nine weeks later, on June 11, and remained under observation for 19 days. The companion is found to have separated from the parent nucleus with a velocity of less than 1 m s−1; subsequently it was subjected to a nongravitational deceleration of 14 units of 10−5 the Sun’s gravitational acceleration. The companion’s overall dimensions can from this value be estimated at less than one hundred meters across. Unlike the primary nucleus, the companion displayed considerable fluctuations in brightness on time scales spanning at least three orders of magnitude, from a fraction of one hour to weeks. The long temporal gap between the companion n’s birth and first detection ap- pears to be a corollary of the brightness variability. Evidence from the light curve suggests that the companion became detectable only because of large amounts of debris that it started shedding as well as increased activity from areas newly exposed by progressive fragmentation, the same process that

also resulted in the companion’s impending disintegration by the end of June or in early July. Subject headings: comets: individual (C/2015 ER61) — methods: data analysis

Precession of the Disk in Pleione  Study of the Hα Line Profile

Ernst Pollmann


Medium-resolution  spectroscopy  of  the  binary  system  Pleione  (28  Tau),  obtained  over  the  time  period  October  2004  (JD  2453300)  to  March  2018  (JD  2458185)  by  the  ARAS  Spectroscopy  Group,  has  been  used  to  determine  the  central  absorption  depth  (CA),  V/R-ratio,  radial  velocity  and  equivalent  width  of  the  Hα  emission,  in  order  to  study  the  disk  precession  as  a  consequence  of  the  periastron  passages  of  the  companion.  We  found  an  exact coincidence of the CA maxima with the minima of V/R and RV as a result of the diskprecession.  This  has  never  before  been  observed  during  the  maximum  shell  phase  in  the  years around 1980, or during the initial shell phase around August/October 1974.  

Recent high-cadence photometry and outburst characteristics of Comet 29P/Schwassmann-Wachmann 1

Richard Miles  - British Astronomical Association, Burlington House, Piccadilly, London, UK,

co-authors: Jean-François Soulier, Tony Angel, Luc Arnold, Jean-Gabriel Bosch, Kim Breedlove, Erik Bryssinck, Paul Camilleri, Montse Campas, Grant Christie, John Drummond, Faustino Garcia, Juan Gonzalez, Kevin Hills, François Kugel, Alain Maury, Jennie McCormick, Gustavo Muler, Ramon Naves, Herbert Raab, Paul Roche, Justin Tilbrook, Jonathan Tuten, and Americo Watkins


Results of high-cadence observations of Comet 29P during 2014–2018 inclusive are presented and the types of outburst characterised. Between 2014 March 03 and 2018 April 24, a total of 59 outbursts were detected and quantified in terms of outburst date and amplitude. The observed frequency corresponds to an average of >12 outbursts p.a. which is much higher than seen in previous years because of the fact that some 46% of the observed events were of less than 1.0 mag amplitude (i.e. mini-outbursts) and so would have essentially been missed by previous observers. Owing to the very high cadence, outburst timing accuracy was extremely good at 0.05d (mode), 0.27d (mean), and 0.34d ( The brightest outburst attained r = 12.1 and the greatest observed amplitude was 5.1 mag. For the first time, 29P was imaged whilst outbursting (on 2017 July 02) and the derived photometry showed the rise from quiescence to half maximum light occurred within only 0.018d. Coma morphologies indicate prograde nuclear rotation.




We present a high-cadence time series of spectroscopic observations of the Hα emission line profile obtained during the egress and total eclipse phases of the M supergiant binary VV Cephei (M2 Iab + B0-2 V) for the 2017-2018 eclipse.  Medium-resolution spectroscopy, obtained at an almost nightly cadence by the ARAS Spectroscopy Group from Apr 2017 through Jun 2018, has been used to construct a time-series of equivalent widths (EWs) of the Hα emission line flux. The peak fluxes of the blue (V) component and the red (R) component relative to the continuum, as well as their ratio V/R, have also been found. We report on a new 43.5-day periodic variation in the Hα emission that is present throughout the entire time series and, in particular, persists through mid-eclipse.


Zdenek Sekanina & Rainer Kracht


A sequence of events, dominated by two outbursts and ending with the preperihelion disintegration of comet C/2017 S3, is examined. The onset times of the outbursts are determined with high accuracy from the light curve of the nuclear condensation before it disappeared following the second outburst.

While the brightness of the condensation was declining precipitously, the total brightness continued to grow in the STEREO-A’s HI1 images until two days before perihelion. The red magnitudes measured in these images refer to a uniform cloud of nuclear fragments, 2200 km2 in projected area, that began to expand at a rate of 76 m s−1 at the time of the second outburst. A tail extension, detected in some STEREO-A images, consisted of dust released far from the Sun. Orbital analysis of the ground-based observations shows that the comet had arrived from the Oort Cloud in a gravitational orbit. Treating positional residuals as offsets of a companion of a split comet, we confirm the existence of the cloud of radiation-pressure driven millimeter-sized dust grains emanating from the nucleus during the second outburst. We detect a similar, but compact and much fainter cloud (or a sizable fluffy dust aggregate fragment) released at the time of the first outburst. — The debris would make a sphere of 140 m across and its kinetic energy is equivalent to the heat of crystallization liberated by 108 g of amorphous water ice. Ramifications for short-lived companions of the split comets and for 1I ‘Oumuamua are discussed.

Evolution of the disk of π Aqr: From near-disappearance to a strong maximum

Author:Yaël Nazé - Groupe d’Astrophysique des Hautes Energies, STAR, Universite de Liege,Belgium

Co-authors: Gregor Rauw, Joan Guarro Fló, Arnold De Bruin, Olivier Garde, Olivier Thizy, Franck Houpert, Ernst Pollmann, Carl J. Sawicki, Marco Leonardi, Malin Moll,

Christoph T. Quandt, Paolo Berardi, Tim Lester, Patrick Fosanelli, André Favaro, Jean-Noël Terry, Keith Graham, Benjamin Mauclaire, Terrence Bohlsen, Michel Pujol,

Etienne Bertrand, Erik Bryssinck, Valérie Desnoux, Patrick Lailly, Jacques Montier, Massimiliano Mannucci, Nico Montigiani, Albert Stiewing, James Daglen, Christian Kreider,

Thierry Lemoult, Tony Rodda


Some Be stars display important variability of the strength of the emission lines formed in their disk. This is notably the case of π Aqr. We present here the recent evolution of the Be disk in this system thanks to spectra collected by amateur spectroscopists since the end of 2013. A large transition occurred: the emission linked to the Be disk nearly disappeared in January 2014, but the disk has recovered, with a line strength now reaching levels only seen during the active phase of 1950–1990. In parallel to this change in strength occurs a change of disk structure, notably involving the disappearance of the strong asymmetry responsible for the V/R modulation.

Monitoring the Hα equivalent width (EW) and V/R of π Aqr

Author: Arnst Polman - 24 co-authors

Dear colleagues, in supplement to the paper of Yael Naze (New Astronomy 73, 2019, 101279) here an up-dated analysis of Halpha EW and V/R since October 2004 It seems of high interest to monitore the star during the following years in terms of evolution of the Halpha maximum and the beginning of clear V/R activity. At present it is almost impossible to determine V/R because of the balanced density within the disk. But the time will come, when local density differences will appear

Dust Environment Model of the Interstellar Comet 2I/Borisov

Authors: G. Cremonese , M. Fulle , P. Cambianica, G. Munaretto, M. T. Capria, M. Lazzarin, A. Migliorini, W. Boschin, G. Milani, A. Aletti,8, G. Arlic, P. Bacci, R. Bacci, E. Bryssinck, D. Carosati, D. Castellano, L. Buzzi, S. Di Rubbo, M. Facchini, E. Guido, F. Kugel, R. Ligustri, M. Maestripieri, A. Mantero, J. Nicolas, P. Ochner, C. Perrella, R. Trabatti, and A. Valvasori


2I/Borisov is the first interstellar comet discovered on 2019 August 30, and it soon showed a coma and a dust tail. This

study reports the results of images obtained at the Telescopio Nazionale Galileo telescope, on La Palma—Canary Islands,

in 2019 November and December. The images have been obtained with the R filter in order to apply our dust tail model.

The model has been applied to the comet 67P/Churyumov–Gerasimenko and compared to the Rosetta dust measurements

showing a very good agreement. It has been applied to the comet 2I/Borisov, using almost the same parameters, obtaining

a dust environment similar to that of 67P/Churyumov–Gerasimenko, suggesting that the activity may be very similar. The

dust tail analysis provided a dust-loss rate Qd≈35 kg s−1 in 2019 November and Qd≈30 kg s−1 in 2019 December.

Seeing the Bigger Picture: Rosetta Mission Amateur Observing Campaign and Lessons for the Future

Authors: Helen Usher , Colin Snodgrass , Simon F. Green , Andrew Norton , and Paul Roche


Amateur astronomers can make useful contributions to the study of comets. They add temporal coverage and multiscale observations that can aid the study of fast-changing and large-scale comet features. We document and review the amateur observing campaign set up to complement the Rosetta space mission, including the data submitted to date, and consider the campaign's effectiveness in the light of experience from previous amateur comet campaigns. We report the results of surveys of campaign participants, the amateur astronomy community, and schools who participated in a comet 46P observing campaign. We draw lessons for future campaigns, which include the need for clarity of objectives; recognizing the wider impact campaigns can have on increasing science capital; clear, consistent, timely, and tailored guidance; easy upload procedures with built-in quality control; and regular communication, feedback, and recognition.

V1405 Cas (= PNV J23244760+6111140) now displaying Fe II emission

Authors: Shore, S. N.; Buil, C.; Dubovsky, P.; Berardi, P.; Bajer, M.; Boussin, C.; Guarrò, J.; Teyssier, F.; Bertrand, E.; Viannet, J. M.; Boyd, D.; Boubault, F.; Allen, H.; Le Lain, M.; le Dû, P.; Cazzato, P.; Coffin, J.; Shank, K.; Bryssinck, E.; Garde, O. Gurney, K.; Leadbeater, R.


We report that the slow nova Cas 2021 (V1405 Cas = PNV J23244760+6111140), discovered in outburst on 2021 Mar 18.4 (CBET #4945, ATel #14471, #14472, #14476, #14478, #14482, #14530) has begun to display Fe II absorption features.

Outbursts and stellar properties of the classical Be star HD 6226

Authors: Noel D Richardson, Olivier Thizy, Jon E Bjorkman, Alex Carciofi, Amanda C Rubio, Joshua D Thomas, Karen S Bjorkman, Jonathan Labadie-Bartz, Matheus Genaro, John P Wisniewski, Luqian Wang, Douglas R Gies, S Drew Chojnowski, Andrea Daly, Thompson Edwards, Carlie Fowler, Allison D Gullingsrud, Nolan Habel, David J James, Emily Kehoe, Heidi Kuchta, Alexis Lane, Anatoly Miroshnichenko, Ashish Mishra, Herbert Pablo, Maurice Peploski, Joshua Pepper, Joseph E Rodriguez, Robert J Siverd, Keivan G Stassun, Daniel J Stevens, Jesica L Trucks, James Windsor, Mackenna Wood, Étienne Bertrand, Jean-Jacques Broussat, Erik Bryssinck, Christian Buil, Stéphane Charbonnel, Arnold de Bruin, Joe Daglen, Valerie Desnoux, James Dull, Olivier Garde, Keith Graham, Kevin Gurney, Alun Halsey, Patrik Fosanelli, Joan Guarro Fló, Franck Houpert, Foster James, Christian Kreider, Robin Leadbeater, Tim Lester, Dong Li, Alain Maetz, Albert Stiewing, Peter Somogyi, Jean-Noël Terry, Stéphane Ubaud, Ulrich Waldschlaeger


The bright and understudied classical Be star HD 6226 has exhibited multiple outbursts in the last several years during which the star grew a viscous decretion disk. We analyse 659 optical spectra of the system collected from 2017-2020, along with a UV spectrum from the Hubble Space Telescope and high cadence photometry from both TESS and the KELT survey. We find that the star has a spectral type of B2.5IIIe, with a rotation rate of 74 per cent of critical. The star is nearly pole-on with an inclination of 13${_{.}^{\circ}}$4. We confirm the spectroscopic pulsational properties previously reported, and report on three photometric oscillations from KELT photometry. The outbursting behaviour is studied with equivalent width measurements of Hα and Hβ, and the variations in both of these can be quantitatively explained with two frequencies through a Fourier analysis. One of the frequencies for the emission outbursts is equal to the difference between two photometric oscillations, linking these pulsation modes to the mass ejection mechanism for some outbursts. During the TESS observation time period of 2019 October 7 to 2019 November 2, the star was building a disk. With a large dataset of Hα and Hβ spectroscopy, we are able to determine the timescales of dissipation in both of these lines, similar to past work on Be stars that has been done with optical photometry. HD 6226 is an ideal target with which to study the Be disk-evolution given its apparent periodic nature, allowing for targeted observations with other facilities in the future.

Comets beyond 4 au: How pristine are Oort nuclei?

the Royal Astronomical Society: published on 3 may 2022

Marco Fulle, M Lazzarin, F La Forgia, V V Zakharov, I Bertini, E Mazzotta Epifani, E Ammannito, A Buzzoni, M T Capria, A Carbognani, V Da Deppo, V Della Corte, S Fiscale, E Frattin, L Inno, A Migliorini, C Pernechele, A Rotundi, G Sindoni, C Tubiana, G Milani, A Aletti, P Bacci, G Baj, F Bellini, E Bryssinck, M Di Grazia, M Facchini, M Feraco, F Kugel, M Maestripieri, D Tirelli, A Valvasori, C Snodgrass, G H Jones


The ESA mission Comet Interceptor will target an Oort or interstellar comet during its first approach to the Sun. Meanwhile, the Vera Rubin LSST Survey will observe hundreds of active comets per month beyond 4 au from the Sun, where water vapor pressure is expected to be too low to eject dust. We discuss observations of dust tails at heliocentric distances larger than 4 au in order to retrieve the physical parameters driving cometary activity beyond Jupiter by means of a probabilistic tail model, which is consistent with the activity model defining the gas coma parameters due to the sublimation of carbon monoxide, molecular oxygen, methane, ethane and carbon dioxide since the activity onset at 85 au from the Sun. We find that: (i) All the observed dust tails are consistent with the adopted activity model; (ii) The tail fits depend on three free parameters only, all correlated to the nucleus size; (iii) Tail fits are always improved by anisotropic dust ejection, suggesting activity of Oort nuclei dominated by seasons; (iv) Inbound seasons suggest cometary activity before the ejection of protocomets into the Oort cloud, as predicted by the activity model; (v) Oort nuclei larger than 1 km may be characterized by a fallout up to ≈100 m thick deposited during ≈60 yr inbound; (vi) On the other side, Oort nuclei smaller than 1 km may appear more pristine than Jupiter Family Comets when observed at 1 au from the Sun.

Comet C/2011 J2 (LINEAR) nucleus splitting: Dynamical and structural analysis

Federico Manzini, Virginio Oldania, Masatoshi Hirabayashi, Raoul Behrend, Roberto Crippa, Paolo Ochner, José Pablo Navarro Pina, Roberto Haver, Alexander Baransky, Erik Bryssinck, Andras Dana, Josè De Queiroz , Eric Frappa, Maylis Lavayssiere.


After the discovery of the breakup event of comet C/2011 J2 in August 2014, we followed the primary body and the main fragment B for about 120 days in the context of a wide international collaboration.

From the analysis of all published magnitude estimates we calculated the comet absolute magnitude H=10.4, and its photometric index n=1.7. We also calculated a water production of only 110 kg/s at the perihelion. These values are typical of a low-activity, long-period or new comet.

Analysis of the motion of fragment B over the observation period showed that the first breakout event likely occurred between 12 July and 30 July 2014. Nucleus B remained persistently visible throughout the 4-month observation period.

The projected separation velocity of nucleus B from the parent body was 4.22 m/s at the time of the breakup and 12.7 m/s at the end of the observation period, suggesting that nucleus B was subjected to a constant deceleration .

The spin period of the main nucleus was estimated as 4.56 h±0.05 h by photometric analysis.

The structural analysis of the comet showed a cohesive strength of the nucleus greater than ~0.9 kPa; assuming a bulk density of 500 kg/m3, with a rotation period of 4.56 h the cometary nucleus might have failed structurally, especially if the body was elongated.

These results suggest that the nucleus of comet C/2011 J2 has an elongated shape, with a ratio of the semi-minor axis to the semi-major axis ; the semi-major axis of the pristine nucleus could be larger than 8 km.

From this study, we propose that rotational disruption, possibly combined with sublimation pressure, was a reasonable explanation for the breakup event in comet C/2011 J2.

Radial Distribution of the Dust Comae of Comets 45P/Honda–Mrkos–Pajdusáková and 46P/Wirtanen(Article)

C. Lejoly, W. Harris, N. Samarasinha, B. E. A. Mueller, E. Howell, J. Bodnarik, A. Springmann, T. Kareta, B. Sharkey, J. Noonan, (4*P Campaign), L. R. Bedin, J.-G. Bosch, A. Brosio, E. Bryssinck, J.-B. de Vanssay, F.-J. Hambsch, O. Ivanova, V. Krushinsky, Z.-Y. Lin, F. Manzini, A. Maury, N. Moriya, P. Ochner and V. Oldani


There was an unprecedented opportunity to study the inner dust coma environments, where the dust and gas are not

 entirely decoupled, of comets 45P/Honda–Mrkos–Pajdusáková ̆ (45P/HMP) from 2016 December 26 to 2017 March 15, and 46P/Wirtanen from 2018 November 10 to 2019 February 13, both in visible wavelengths. The radial profile slopes of these comets were measured in the R and HB-BC filters most representative of dust, and deviations from a radially expanding coma were identified as significant. The azimuthally averaged radial profile slope of comet 45P/HMP gradually changes from −1.81 ± 0.20 at 5.24 days preperihelion to −0.35 ± 0.16 at 74.41 days postperihelion. Contrastingly, the radial profile slope of 46P/Wirtanen stays fairly constant over the observed time period at −1.05 ± 0.05. Additionally, we find that the radial profile of 46P/Wirtanen is azimuthally dependent on the sky-plane-projected solar position angle, while that of 45P/HMP is not. These results suggest that comets 45P/HMP and 46P/Wirtanen have vastly different coma dust environments and that their dust expansion properties are distinct. As evident from these two comets, well-resolved inner comae are vital for detailed characterization of dust environments.



Y. Nazé, J. Guarro Flo, A. Leduc, A. Stiewing, S. Curry, X. Dupont, E. Bryssinck, H.R. Diz, E. Bertrand, C. Buil, V. Desnoux,

O. Garde


ζ Tau is a well known binary comprising a Be star. Its decretion disk changes with time and we report here on the latest variability behaviour thanks to new amateur data.

The cyclic variability observed in the previous years and dominated by the modulated centralabsorption continues. Only little asymmetries are detected for the Hα line