# A rotational age for the open cluster NGC 2281

**Authors:** D. J. Fritzewski, S. A. Barnes, J. Weingrill, T. Granzer, E. Cole-Kodikara, K. G. Strassmeier  
**arXiv:** [2305.03755](https://arxiv.org/abs/2305.03755)  
**Date:** 2023-05-05  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2305.03755v1/

## Key points

- The study aimed to estimate the age of the open cluster NGC 2281 using rotational properties of its low-mass members
- Previous age estimates for this cluster ranged from 275 Myr to 630 Myr
- Rotation periods were measured for 126 cool star members over an eight-month photometric time series obtained at the 1.2 m robotic STELLA telescope in Tenerife
- A rich color-period diagram was constructed for NGC 2281 with very few outliers above the slow rotator sequence and an evolved fast rotator sequence was identified that can be used to accurately age date the open cluster relative to other open clusters
- Comparisons with M37 and M48 showed that all three open clusters are roughly coeval, and the authors estimated the age of NGC 2281 to be $435\pm50$ Myr
- Spin-down rates of mid-K and early-M fast rotators are significantly lower than those for early-K stars, and spin-down of early-K fast rotators might be governed by an additional mass dependence
- An example overview diagram was provided for every star in their study, showing full and phase-folded light curves for each exposure setting (V 24 s, V 120 s, Ic 600 s) as well as four periodograms for each exposure setting.
- Membership information for NGC 2281 is listed in Table 1
- ArXiv Query search results including article number/page number (5/14), cID (3120 NW), GG RP (0=0.955), G (16.355), and P (3.14±0.0115) were provided

## Summary

In this study, the authors aimed to estimate the age of the open cluster NGC 2281 using rotational properties of its low-mass members. Previous age estimates for this cluster ranged from 275 Myr to 630 Myr. The authors measured rotation periods for 126 cool star members (70% of observed members) over an eight-month photometric time series obtained at the 1.2 m robotic STELLA telescope in Tenerife. They constructed a rich color-period diagram for NGC 2281 with very few outliers above the slow rotator sequence and identified an evolved fast rotator sequence that can be used to accurately age date the open cluster relative to other open clusters. Comparisons with M37 and M48 showed that all three open clusters are roughly coeval, and the authors estimated the age of NGC 2281 to be $435\pm50$ Myr. Through comparisons with younger NGC 3532 and older Praesepe, they determined that spin-down rates of mid-K and early-M fast rotators are significantly lower than those for early-K stars. Additionally, they suggested that spin-down of early-K fast rotators might be governed by an additional mass dependence. The authors also provided an example overview diagram for every star in their study, showing full and phase-folded light curves for each exposure setting (V 24 s, V 120 s, Ic 600 s) as well as four periodograms for each exposure setting. They marked best periods with orange lines and gave their values at left while marking finally chosen periods with blue lines noted in text in center; width of blue line indicated period uncertainty. Finally, Table 1 listed membership information for NGC 2281 while a feed provided ArXiv Query search results including article number/page number (5/14), cID (3120 NW), GG RP (0=0.955), G (16.355), and P (3.14±0.0115).