Complex periodic variables (CPVs) are stars that exhibit highly structured and periodic optical light curves. Previous studies have indicated that these stars are typically disk-free pre-main-sequence M dwarfs with rotation periods ranging from 0.2 to 2 days. To advance our understanding of these enigmatic objects, we conducted a blind search using TESS 2 minute data of 65,760 K and M dwarfs with T<16 mag and d<150 pc. We found 50 high-quality CPVs, and subsequently determined that most are members of stellar associations. Among the new discoveries are the brightest (T ≈ 9.5 mag), closest (d ≈ 20 pc), and oldest (≈200 Myr) CPVs known. One exceptional object, LP 12-502, exhibited up to eight flux dips per cycle. Some of these dips coexisted with slightly different periods, and the shortest-duration dips precisely matched the expected timescale for transiting small bodies at the corotation radius. Broadly, our search confirms that CPVs are mostly young (≲150 Myr) and low-mass (≲0.4 M⊙). The flux dips characteristic of the class have lifetimes of ≈100 cycles, although stellar flares seem to induce a sudden dip collapse once every few months. The most plausible explanation for these phenomena remains corotating concentrations of gas or dust. The gas or dust is probably entrained by the star's magnetic field, and the sharp features could result from a multipolar field topology, a hypothesis supported by correspondences between the light curves of CPVs and of rapidly rotating B stars known to have multipolar magnetic fields.
Transient Corotating Clumps around Adolescent Low-mass Stars from Four Years of TESS
Abstract
Copyright and License
© 2023. The Author(s). Published by the American Astronomical Society.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
L.G.B. is grateful for support from the Heising-Simons 51 Pegasi b Fellowship, from the NASA TESS GI Program (G06030), and for helpful conversations with J. Spake, A. Mann, G. Laughlin, and B. Draine. We are also grateful for the assistance of S. Yee, L. Weiss, H. Isaacson, and A. Howard in acquiring and reducing the High Resolution Echelle Spectrometer (HIRES) spectra, and for the reviewer's suggestion to consider the proximity of the dip and spot periods. This paper relied primarily on data collected by the TESS mission; the specific 2 minute cadence observations can be accessed via doi:10.17909/t9-nmc8-f686. Funding for the TESS mission is provided by NASA's Science Mission Directorate. We thank the TESS Architects (G. Ricker, R. Vanderspek, D. Latham, S. Seager, and J. Jenkins) and the many TESS team members for their efforts to make the mission a continued success. LP 12-502 in particular was observed at 2 minute cadence thanks to the TESS Guest Investigator programs G022252 (PI: J. Schlieder; Sectors 18, 19, 25, 26) and G04168 (PI: R. Jayaraman; Sector 53). A.D.U. acknowledges support by NASA under award number 80GSFC21M0002, as well as ROSES award 22-ADAP22-0070.
L.G.B. conceived the project, performed the dip-counting search, light-curve classification, cluster membership, SED, variability, and secondary-period analyses, and wrote the manuscript. R.J. and S.R. performed the Fourier-based analysis and contributed to light-curve classification. L.R. cross-examined the light-curve classification, and contributed an independent SED analysis. A.D.U. identified the magnetic B star connection. L.A.H. contributed to project design. J.N.W., S.R., and L.A.H. significantly improved the clarity of the manuscript. G.Á.B. acquired and maintained the servers used to run the dip-finding pipeline.
Facilities
Astrometry: Gaia (Gaia Collaboration et al. 2018, 2023) - . Imaging: Second Generation Digitized Sky Survey - . Spectroscopy: Keck I (HIRES; Vogt et al. 1994) - . Photometry: TESS (Ricker et al. 2015) - , roadband photometry: 2MASS (Skrutskie et al. 2006) - , APASS (Henden et al. 2016) - , Gaia (Gaia Collaboration et al. 2018, 2023) - , SDSS (York et al. 2000) - , WISE (Wright et al. 2010; Cutri et al. 2021) - .
Software References
astrobase (Bhatti et al. 2021), astropy (Astropy Collaboration et al. 2013, 2018, 2022), lightkurve (Lightkurve Collaboration et al. 2018), numpy (Harris et al. 2020), pyGAM (Servén & Brummitt 2018), scipy (Virtanen et al. 2020), TESS-point (Burke et al. 2020), wotan (Hippke et al. 2019).
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Additional details
- Heising Simons Foundation
- 2021-2890
- National Aeronautics and Space Administration
- G06030
- National Aeronautics and Space Administration
- G022252
- National Aeronautics and Space Administration
- 80GSFC21M0002
- National Aeronautics and Space Administration
- 22-ADAP22-0070
- Accepted
-
2023-11-06Accepted
- Available
-
2023-12-28Published
- Caltech groups
- Astronomy Department
- Publication Status
- Published