GROWTH Collaboration

Astrometry with Streaking Stars: Astreaks!

As the proper motion of the target Near Earth Object (NEO) increases from a couple of arc-seconds to tens of arc-seconds per minute, non-sidereal observations lead to streaking background reference stars which make the end goal of accurate astrometry very challenging. The existing source extraction software are not designed to detect sources with tens or hundreds of arc-seconds of elongation. I have developed a fully automated, robust and modular pipeline, Astreaks, that does reliable and accurate astrometry of non-sidereal data, where the reference stars have significant elongation. Robustness of source extraction process to generate a catalogue of objects is of utmost importance in astrometry. Astreaks achieves this goal by analyzing calibrated non-sidereal data in the following steps: sky background estimation, streak spread function (SSF) model generation for reference stars, thresholding, image segmentation and source deblending, synthetic image generation, getting astrometry solution, and getting astrometry and photometry of the target. The detailed implementation, modularity, and validation of Astreaks have been discussed at the GROWTH India Telescope official website. The results from this pipeline have also been presented at the Europlanet Science Congress 2021. Stay tuned for the official release of Astreaks!

Outbursts of Comet 67P/Churyumov-Gerasimenko

Comet 67P/Churyumov-Gerasimenko moved past its perihelion on 2021 November 02.057 UTC. The European Science Agency's Rosetta Mission monitored this comet close to its previous perihelion and observed several mini-outbursts occurring every ~29 hours. However, very few outbursts were observed in ground-based data during the same apparition. We monitored this comet using the GROWTH-India Telescope close to its November 2021 perihelion to gather additional evidence for its outbursts. We discovered two intense outbursts of this comet with total outburst dust mass ejected comparable to the strongest outbursts observed by Rosetta mission. The detailed morphology analysis and outburst mass are discussed in a Research Note of the AAS. The figure below shows our lightcurve with the two outbursts marked at nearly -3 and +15 days from the perihelion.

Activity of Comet 29P/Schwassmann-Wachmann

Comet 29P/Schwassmann-Wachmann 1 is known for showing furious activity. While usually hovering around 16th magnitude, it tends to blow up to 12th magnitude. I am lucky to have witnessed one such event in October'2021. The gif shows the ejecta after this major outburst. Following this, we also observed another outburst with a strength of ~0.22 magnitude.

Main-Belt Active Asteroid 2005 QN173

The main-belt asteroid, 2005 QN173, was discovered to have turned on its tail in July'2021. I did multi-band imaging of this active asteroid with GROWTH India Telescope to measure its colours, in coordination with the GROWTH collaboration. I obtained multiple 300-second exposures and stacked them over the main-belt asteroid. Its long magnificent tail is clearly visible in the stacked images.

Comet Outbursts

I have observed 10+ cometary outbursts with GROWTH India Telescope. The carousel includes light curves of 4 of the outbursting comets observed with Growth India Telescope, Zwicky Transient Facility, Las Cumbres Observatory and SLT. Two outbursts of Comet 7P/Pons-Winnecke, discovered by ZTF and GIT respectively, and confirmed with GIT, ZTF and SLT data, with observations starting on 2021-05-21.701 UT. The two outbursts of Comet 29P/Schwassmann-Wachmann 1 were observed with GIT and ZTF, starting on 2021-03-23.128 UT. The three outbursts of comet C/2020 R4, discovered in ZTF data with observations starting on 2021-04-18.436 UT. The second and third outbursts were followed up with GIT. Outbursts of comet C/2020 R4 in June 2021, observed with ZTF, GIT and LCO, starting on 2021-06-02.208 UT.

Episodically Active Asteroid (6478) Gault

Active asteroids are objects which eject dust, producing transient, comet-like comae and tails with semimajor axes interior to Jupiter and Tisserand parameter with respect to Jupiter greater than 3. Scientific interests for their studies include their numerous activity mechanisms (including ice sublimation, thermal disintegration, impact ejection and disruption, rotational instabilities and many more), surface properties, orbital evolution and distribution. (6478) Gault is dynamically a main-belt asteroid with Tisserand parameter of 3.46. What makes Gault interesting is that it has an extensive history of cometary activity and its activity mechanism was not fully known. After the confirmation of quiescent state of Gault, as it moved out of solar conjunction in June 2020, coordinated observations using the GROWTH network and other facilities were planned to constrain its rotation period. With the help of coordinated observations, a rotation period of ~ 2.5 hr was constrained, which is also the critical rotation period of a body of the size of Gault. It was concluded that the activity of Gault was due to surface mass shedding from its fast rotation spun up by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect. The details of this collaborative effort have been presented in Josiah N. Purdum et al 2021 ApJL 911 L35.

Follow-up of Comets

I have been following up possible comet candidates to report their cometary activity and features. Since the comets are usually very faint, stacking is needed to reveal their cometary features. For stacking data over the comets, I had been using the "Track and Stack” operation in the software Astrometrica, until I developed a fully-automated version of the same, which I call "Tracery". The image on the left dispays the results from Tracery on the Comet C/2021 A4 (NEOWISE) data acquired with GROWTH India Telescope. The comet had a sky plane motion of 1.33′′/min at a position angle of 342.9◦. Stacking lead to a more than 3−fold amplification in the signal-to-noise ratio of the comet. The left plot indicates the O-C residuals in the X and Y direction of all positions of comets observed with GROWTH India Telescope. The data was acquired using non-sidereal tracking. The comets tracked had a proper motion in the range 0.2−2′′ /min. The exposures of 300 s were taken, resulting in negligible elongation in the reference stars. Astrometry on this data was performed using the Track and Stack method in software Astrometrica, with a standard deviation of 0.49′′

Follow-up of Near-Earth Objects

I have done optical follow-up of 50+ possible Near-Earth Objects candidates with the GROWTH-India Telescope. All of them were non-sidereally tracked. This plot is an (a, e, i) orbital distribution of all solar system objects I have observed. The NEOs are marked with circles, Main-Belt objects with pentagons and comets with crosses. The region between perihelion q = 1.3 AU and aphelion Q = 0.983 AU demarcates the NEO regime. We have observed 5 Atens, 28 Apollos and 17 Amors. The periodic comets with a > 4 AU and non-periodic comets are not included here. We have also observed 5 Inner Main Belt Asteroids, 5 Central Main Belt Asteroids and 7 Outer Main Belt Asteroids.

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