An open cluster in the TESS CVZ: gyrochronology and δ Scuti stars in NGC1901
Bernizzoni, Mara; Bedding, Tim; Mani, Prasad; Montet, Benjamin; Crawford, Courtney
- Publisher
- Zenodo
- Language
- en
Abstract
An open cluster consists of stars sharing the same age, distance and initial metallicity. Characterising its members deepens our understanding of stellar formation and evolution. NGC1901 is an 891-Myr-old open cluster confirmed using Gaia data and located in the TESS southern continuous viewing zone (CVZ). It is the third cluster discovered within this region, enabling a thorough investigation due to extensive available data. Our main goal is to measure the most precise age estimate of this cluster to date, using both gyrochronology and asteroseismology. Age-dating an open cluster is challenging, as different methods often yield different values. Similar analysis of UBC-1, another CVZ cluster, by Fritzewski et al. (2024), suggests how promising the approach is. Long-duration TESS observations allow accurate measurements of rotation periods, and this is the first time NGC1901 is comprehensively characterised. As a preliminary task, we refine the NGC1901 membership list using spatial and kinematic filtering of Gaia DR3 data, and compare it to that from Hunt & Reffert (2023). We explore stellar lightcurves from TESS cycles 1, 3 and 5 to search for brightness variability indicative of rotation. The next step involves deriving the cluster's age through gyrochronology, a technique based on how rotation periods evolve with time. G, K and M-type dwarfs experience strong magnetic braking, and therefore spin down as they age. When plotted as function of colour, rotation periods highlight age-dependent sequences. In this context, we compare NGC1901's distribution to those of NGC6811 and Praesepe, which are 1 Gyr (Curtis et al. 2019) and 670 Myr old (Rampalli et al. 2021), respectively. Moreover, we examine A and F-type main sequence stars for variability and use asteroseismology to identify potential g-mode and p-mode pulsators. Period-spacing patterns from g-mode pulsators offer another extremely precise constraint on stellar ages. Combining gyrochronology of low-mass G/K dwarfs with asteroseismology of higher-mass A/F stars can enhance the precision of NGC1901's age estimate.
Full text
Conclusion future work •38 stars show a periodicity comparable to that expected •Their colour-rotation period distribution suggests that modelling the cluster rotation sequence could better constrain NGC1901’s age •Compare the results to that from other age estimators Future work •Examination of A and F-type main sequence stars for variability •Use asteroseismology to study g-mode and pmode pulsators An old open cluster in the TESS CVZ: gyrochronology and 𝛿 Scuti stars in NGC1901 Mara Bernizzoni1, Timothy R. Bedding1, Prasad Mani1, Benjamin Montet2, Courtney L. Crawford1 1Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006, Australia; 2School of Physics, University of New South Wales, Sydney, NSW 2052, Australia Mara’s email: [email protected].edu.au References: [1] Bouma L. G. et al. (2023) | [2] Cantat-Gaudin T. et al. (2020) | [3] Curtis J. L. et al. (2019) | [4] Douglas S. T. et al. (2019) | [5] Fritzewski D. J. et al. (2024) | [6] Hunt & Reffert (2023) | [7] Li G. et al. (2024) | [8] Mani et al. (2025) | [9] Rampalli R. et al. (2021) Fig 2: eleanor lightcurve (upper panel), periodogram (lower left panel) and phase-folded lightcurve from cycle 5 only (lower right panel) for TIC 231122546. Measuring rotation periods •Long-duration TESS observations allow accurate measurements of rotation periods •Exploration of stellar lightcurves from TESS cycles 1, 3 and 5 looking for rotation signal •Lightcurves analysis from 123 stars across multiple TESS sectors, using TESS-SPOC and eleanor pipelines •To optimise the rotation signal detection we combined data from both pipelines, giving preference to TESS-SPOC where available •Measurement of rotation periods from Lomb-Scargle periodograms NGC1901 •An ~890-Myr-old [2] open cluster within the TESS southern CVZ •Neglected for a long time, due to its proximity to the LMC on the sky •we refined its membership list using spatial and kinematic filtering of Gaia DR3 data. We found 143 confirmed [6] and candidate members. Our goals •Characterisation of NGC1901’s members to deepen our understanding of stellar formation and evolution. •Get the most precise age estimate to date, using both gyrochronology and asteroseismology → challenging task, as different age-dating methods often yield different values, as shown for NGC2516 [7] and UBC-1 [5] Fig 1: sky position (left) and proper motion (right) diagram for NGC1901. Future work: 𝛿 Scuti pulsators Fig 4: Left: zoomed-in colour-magnitude diagram of NGC1901 showing 𝛿Scts. Right: amplitude spectrum of selected stars. TIC 40346830 is a 𝛿Sct-𝛾Dor hybrid. Gyrochronology of open clusters •Rotation periods evolve with time •G, K and M-type dwarfs experience strong magnetic braking, spinning down as they age •When plotted as function of colour, rotation periods highlight agedependent sequences •The colour-rotation relation is calibrated using open clusters [1] [4] •There are very few old clusters of this age that have good gyrochronology references. NGC1901 represents an additional sequence to this diagram. Fig 3: gyrochronology diagram showing the colour-rotation period distribution of NGC1901, compared to NGC6811 and Praesepe, respectively older and younger than the expected gyrochrone for NGC1901. We mark and label the star that is shown in details in Fig 2.
