Kent Academic Repository Full text document (pdf) Citation for published version Evitts, Jack J (2020) An analysis on the photometric variability of V 1490 Cyg. Master of Science by Research (MScRes) thesis, University of Kent,. DOI Link to record in KAR https://kar.kent.ac.uk/80982/ Document Version UNSPECIFIED Copyright & reuse Content in the Kent Academic Repository is made available for research purposes. Unless otherwise stated all content is protected by copyright and in the absence of an open licence (eg Creative Commons), permissions for further reuse of content should be sought from the publisher, author or other copyright holder. Versions of research The version in the Kent Academic Repository may differ from the final published version. Users are advised to check http://kar.kent.ac.uk for the status of the paper. Users should always cite the published version of record. Enquiries For any further enquiries regarding the licence status of this document, please contact: [email protected] If you believe this document infringes copyright then please contact the KAR admin team with the take-down information provided at http://kar.kent.ac.uk/contact.html UNIVERSITY OF KENT CENTRE FOR ASTROPHYSICS AND PLANETARY SCIENCE SCHOOL OF PHYSICAL SCIENCES An analysis on the photometric variability of V 1490 Cyg Author: Jack J. Evitts Supervisor: Dr. Dirk Froebrich Second Supervisor: Dr. James Urquhart A revised thesis submitted for the degree of MSc by Research 10th April 2020 Abstract Variability in Young Stellar Objects (YSOs) is one of their primary characteristics. Long- term, multi-filter, high-cadence monitoring of large samples aids understanding of such sources. Although data from the HOYS citizen science project allows for such monitoring, usage of different filters introduces colour-terms to the photometric data. This thesis outlines the development of a novel colour-term correction method, im- proving photometric error to within a couple of percent. The corrected light curve for the YSO, V 1490 Cyg , is then discussed in detail. The source is observed to be a quasi-periodic dipper with a period of 31.447 ± 0.011 days. Long and short-term variability is observed for B, V, Rc and Ic data, with larger variability on short timescales for U and Ha . U amplitudes were observed to vary on timescales of hours, indicating the source is still accreting. No significant trends were observed in the structure function, with the amount of mass in the occulting structure seen to vary by up to a factor of 10 for both mass increase and decrease. The lower esti- −10 mate of the typical accretion rate of V 1490 Cyg was found of the order 10 M /year, consistent with low levels of accretion as seen in other T-Tauri stars. Investigating the orbiting structure in V vs. V − Ic parameter space suggests low column density mate- rial with roughly ISM dust properties. Embedded in this envelope are denser, small- scale structures, most likely composed of larger dust grains. The scattering properties of this material are consistent and do not change over time. An accurate distance to +70 both IC 5070 and V 1490 Cyg of 870 −55 pc has been determined using Gaia. Litera- ture near-infrared (NIR) and mid-infrared (MIR) data suggest that V 1490 Cyg is most likely a CTTS, with a currently low, but variable accretion rate. It is potentially at the start of the transition into a WTTS or transition disk object. This thesis finds the nature of the variability of the source is most likely attributed to a protoplanet-induced disk warp. Acknowledgements This thesis has only become a reality with the kind support and help of many individ- uals. I would like to extend my sincere thanks to all of them. Firstly, I would like to thank all contributors of data for their efforts towards the success of both the HOYS project and this study. Also many thanks to my fellow researchers who have helped in obtaining and discussing the data that is the backbone of this work. In particular I would like to express my special gratitude and thanks to my supervisor, Dr. Dirk Froebrich for imparting his knowledge and expertise. I am highly indebted to both STFC (Grant no. ST/S505456/1) and the University of Kent for the funding that has enabled me to start and continue with this research. Finally, I wish to thank and acknowledge my loving and supportive wife, Liz. Without her help, I could not have succeeded in this endeavour. Declaration of Authorship I, Jack J. Evitts declare that this thesis titled "An analysis on the photometric variability of V 1490 Cyg" and the work presented in it are my own and has been generated by me as the result of my own original research. I confirm that: 1. This work was done wholly or mainly while in candidature for a research degree at this University; 2. Where any part of this thesis has previously been submitted for a degree or any other qualification at this University or any other institution, this has been clearly stated; 3. Where I have consulted the published work of others, this is always clearly at- tributed; 4. Where I have quoted from the work of others, the source is always given. With the exception of such quotations, this thesis is entirely my own work; 5. I have acknowledged all main sources of help; 6. Where the thesis is based on work done by myself jointly with others, I have made clear exactly what was done by others and what I have contributed myself. Signed: Jack J. Evitts Date: 10th April 2020 A summarised version of the data and analysis presented in this thesis has been written into a journal paper that has been submitted to, and accepted by, Monthly Notices of the Royal Astronomical Society for publication. Contents 1 Introduction 3 1.1 Star Formation . .4 1.2 Disks . .5 1.3 Planet Formation . .6 1.4 Variable Young Stars . .7 2 HOYS 10 2.1 The Project . 10 2.2 The Beacon Observatory . 11 2.3 Targets . 12 3 Observational Data and Photometric Calibration 13 3.1 V 1490 Cyg Imaging Observations . 13 3.2 Photometry Data Calibration . 13 3.2.1 Basic Relative Photometric Calibration . 14 3.2.2 Photometry Colour Correction . 15 3.3 Spectroscopy Data . 21 4 Analysis of the Data for the Light Curve of V 1490 Cyg 26 4.1 The Quasi-Periodic Light Curve of V 1490 Cyg . 26 1 4.2 Asymmetry of the Light Curve of V 1490 Cyg . 34 4.3 Analysis of the Variability Fingerprints . 35 4.4 Column Density Distribution of Consecutive Dips . 39 4.5 Colour Dependence of Periodic Dips . 49 5 Discussion 54 5.1 Distance of V 1490 Cyg . 54 5.2 Potential Binarity of V 1490 Cyg . 57 5.3 Literature NIR and MIR data for V 1490 Cyg . 58 5.4 Evolutionary Stage of V 1490 Cyg . 58 5.5 The Nature of V 1490 Cyg . 60 5.5.1 Protoplanet-induced Disk Warp . 61 5.5.2 Magnetically-induced Disk Warp . 61 5.5.3 Hill Sphere of Accreting Protoplanet . 62 6 Conclusions 63 Bibliography 76 A Appendix A: Description of Observatories and Data Reduction 77 A.1 Description of Amateur Observatories and Data . 77 A.2 Description of University and Professional Observatories . 86 2 Introduction Young stellar objects (YSOs) were initially discovered by their irregular and large op- tical variability (Joy, 1945). Their fluxes can be affected by a wide variety of physical processes, such as changeable emission from accretion shocks, variable emission from the inner disk, and variable extinction along the line-of-sight (Carpenter et al., 2001). Furthermore, variability in YSOs occurs on a wide variety of timescales. These can range from short term accretion rate changes over minutes, to long term outburst or disk occultation events, spanning in duration from years to tens of years. Thus, ob- serving variable young stars over a wide range of timescales and wavelengths allows us to explore the physical processes, structure and evolution of their environment, and provides key insights into the formation of stars. Numerous photometric variability surveys have been been conducted in the past, aim- ing to address the study of YSO variability. Often they have either focused on high cadence over relatively short periods (e.g. with COROT and Kepler (Cody et al., 2014; Ansdell et al., 2016)), or more long term, but lower cadence (e.g. with UGPS and VVV (Contreras Peña et al., 2014, 2017b)). The recently initiated HOYS project aims to per- form high cadence, long-term and multi-filter optical monitoring of YSOs. It uses a combination of professional, university and amateur observatories (Froebrich et al., 2018a) to study accretion and extinction related short and long-term variability in a number of nearby young clusters and star forming regions. More detail on the project is discussed in Chapter 2. Characterising the structure and properties of the inner accretion disks in YSOs is vital for our understanding of the accretion processes and the formation of terrestrial (in- ner) planets in those systems. However, investigating the innermost disk structure of YSOs on scales below 1 AU is currently only possible through indirect methods such as photometric monitoring of disk occultation events. Of particular interest are periodic, or semi-periodic, occultation events (e.g. in AA Tau (Bouvier et al., 1999) or UX Ori (Herbst and Shevchenko, 1999) type objects, though often aperiodic). They allow us to identify the physical location of the occulting structures in the disks based on the period, and therefore to determine the spatial scales of the material directly.