Online material

Appendix A: Individual stars

A.1. ϵ + η Cha

GSC 9419-01065: the rotation period derived from our analysis is P = 8.0 d. Although the flux rotational modulation is clearly found in more than five segments; however, the computed v_eq = 2πR/P is inconsistent with the measured vsini = 18.0 km s^-1 (Torres et al. 2006), so this period is considered uncertain. However, we note that the only available vsini measurement has quite a large  ± 30% uncertainty. More accurate determinations would be desiderable to confirm the correctness of the current vsini value.

HD 104237E: the ASAS photometry did not allowed us to infer any periodicity. We adopted the period of P = 2.45 d detected by Feigelson et al. (2003), which combined with the estimated radius gives an equatorial velocity consistent with the measured vsini. This star belongs to a quintuple system, where the brightest component is the Herbig Ae star HD 104237. Feigelson et al. (2003) found a reddening A_V = 1.8 ± 0.3 that likely arises from material within the parent stellar system, the reddening of other members associated to ϵ Cha being small or even absent.

GSC 9416-1029: Doppmann et al. (2007) report a period of P = 5.35 d that likely represents the system’s orbital period. The available ASAS photometry of this star, which is quite inaccurate owing to the target’s faintness, shows evidence of a period P = 5.50 d in two of nine time segments. In the case this is the correct rotational period, which would imply a rotational/orbital synchronisation, which is quite a surprising circumstance at an age of about 6 Myr.

GSC 9235-01702: it has very recently been discovered to be a member of ϵ Cha by Kiss et al. (2011) as part of the RAVE project. From the ASAS photometry, we found the same rotation period as found by Bernhard et al. (2009), based on the same ASAS data.

RECX 1 (EG Cha): we detect a rotation period P = 4.5 d in 12 of 15 time segments, which is twice the period reported by Lawson et al. (2001). An inspection of Fig. 2 of Lawson et al. (2001) shows that their phased light curves in both 1999 and 2000 seasons exhibit significant magnitude phase dispersion.

RECX 11 (EP Cha): we found a period P = 4.84 d in 7 of 12 time segments with confidence level over 99% and no evidence of any power peak at the period P = 3.95 d discovered by Lawson et al. (2001) in 1999 (P = 3.69 d in 2000). Again, an inspection of their phased light curves shows significant dispersion

RECX 12 (EQ Cha): the star shows two significant periods in Lawson et al. (2001), P = 1.25 d and P = 8.55 d. The star is a close binary, so they might represent the rotational periods of the two components. Our analysis allowed us to detect only the shorter period that is adopted in the present analysis.

RECX 15 (ET Cha): is a classical T Tauri star, with evidence of on going accretion (Lawson et al. 2002). The large amplitude variations (up to 0.44 mag) are likely driven by accretion hot spots.

A.2. Octans

CD-58 860: we find two periods, P = 1.612 d and P = 2.610 d, in eight out of ten time segments with comparable levels of confidence. However, the longer period, once combined with stellar radius, determines a ratio vsini/v_eq slightly greater than unity. Therefore, in the present analysis we adopt P = 1.612 d.

CD-43 1451: this star is also present in the SuperWASP archive. However, neither from the ASAS nor from the SuperWASP database we could determine the rotation period, but only the presence of light variability.

HD 274576: the period P = 2.22 d is found in nine out of ten time segments of ASAS photometry and in two out of two SuperWASP observation seasons, and it is fully consistent with the measured vsini. We note that in both the ASAS and SuperWASP timeseries another period P = 1.824 d is also found with a very high confidence level, although it is smaller than the earlier, in almost all time segments, which is also consistent with vsini.

TYC 7066 1037 1: the period P = 2.47 d is found in 6 out of 14 time segments of ASAS photometry and in three out of five segments of SuperWASP photometry.

A.3. Argus and IC 2391

HD 5578 (BW Phe): is a close visual binary. We found two rotation periods of comparable power, P = 1.461 d and P = 3.15 d, in most time segments. The shorter period is assumed to be the star’s rotation period, since it is the only one consistent with a vsini/v_eq ≤ 1.

CD-56 1438: we detect a period P = 0.24 d in only one segment that may conciliate with the very high vsini.

CD-28 3434: the P = 3.82 d period is very well established and also detected in three out of three time segments of SuperWASP data, as well in the complete timeseries. Although no vsini is available to check consistency with v_eq, it is considered a confirmed period.

HD 61005: has been suggested to be a likely member of the Argus association (Desidera et al. 2011). Although its P = 5.04 d period is found in only three time segments of the ASAS timeseries, it was confirmed by the period search carried out in the Tycho and Hipparcos photometry (Desidera et al. 2011), so it is considered confirmed in the present analysis.

CD-39 5883: the period is detected in two out of nine segments of ASAS photometry and in five out of five segments of WASP data as well in the complete timeseries and is consistent with vsini/v_eq ≤ 1.

CD-58 2194: the most significant period is P = 5.16 detected in four time segments as well in the complete timeseries. However, it is inconsistent with the high vsini. It may be the beat of the P = 0.55 d period detected in only one season. This period is therefore considered uncertain.

CD-57 2315: it is variable, but no periodicity was found.

CPD-62 1197: the most significant period is P = 1.26 d which is found in seven out of nine segments. However, it leads to a vsini/v_eq ~ 2 and therefore it will not be considered in the following analysis. Another significant period is P = 0.82 d, which is, however only detected in three out of nine segments, so it is classified as uncertain.

TYC 7695 0335 1: the same P = 0.39 d is found in three out of nine ASAS segments and in four out of four segments of SuperWASP data.

HD 85151A: is a close visual binary. The P = 0.97 d is only found in the ASAS complete timeseries, but in five out of five time segments of SuperWASP data.

CD-65 817: is a close visual binary.

HD 310316: is a close visual binary.

CD-74 673: is a spectroscopic binary with an orbital period P = 614 d (Guenther et al. 2007).

CD-52 9381: the most significant period is P = 5.19 d detected in six out of nine time segments, as well in the complete series. However, a P = 0.89 d is also detected and reported in the ACVS. The shorter one is consistent with vsini/v_eq ≤ 1, and it is considered as a confirmed period.

PPM 351: the most significant period is P = 1.931 d that is found in six out of nine segments; however, it gives vsini/v_eq > 1. Another detected period is P = 0.69 d, which is, however, found in only three out of nine segments, so it is considered uncertain.

PMM 1083 (V365 Vel): our period determination is in good agreement with the earlier determination by Patten & Simon (1996). Two different vsini values are reported in the literature, vsini = 43 km s^-1 from Marsden et al. (2009) and vsini = 67 km s^-1 from Platais et al. (2007). However, only the first is consistent with vsini/v_eq ≤ 1.

PMM 1820 (V366 Vel): our period determination is in good agreement with the earlier determination by Patten & Simon (1996).

PMM 4413: is an SB2 with an orbital period P = 90.6 d (Platais et al. 2007) whose components have measured vsini of 8.6 and 8.4 km s^-1, which give consistent vsini/v_eq ratios.

PMM 4467 (V364 Vel); PMM 4902; PMM 5884 (V377 Vel): our period determinations are in good agreement with the earlier determinations by Patten & Simon (1996).

PPM 8145: unlike stars whose variability arises from dark spots, this star spends most of its time in its fainter state. The variability likely arises from magnitude outbursts. It shows the largest variability amplitude (~2 mag) in our sample. The reference magnitude, differently than other stars, is probably the faintest one.

PMM 4902 (V379 Vel): although detected in only three time segments, it is considered confirmed because its period is confirmed by the literature value (Patten & Simon 1996).

PPM 2182: we found two significant periods, P = 3.28 d and P = 1.437 d. However, both are not consistent with vsini/v_eq ≤ 1, being vsini = 78 km s^-1 (da Silva et al. 2009) and therefore are considered uncertain.

Appendix B: New/revised periodicities in young associations studied in Paper I

The availability of SuperWASP light curves allowed us to revisit some of the targets studied in Paper I. We found SuperWASP timeseries for 71 targets listed in Paper I. For the seven candidate members of β Pic and Tuc/Hor newly proposed by Kiss et al. (2011), we retrieved SuperWASP timeseries for two of them and ASAS time series for the remaining five. Unfortunately, of 78 targets the data on nine stars turned out to be too sparse to be suitable for a meaningful period search. The analysis of the 69 timeseries allowed us to discover (i) 15 new periods (5 of which likely), (ii) to confirm 35 periods, and (iii) to revise 13 periods. Finally, for six stars we could not detect any period. Three of them were also found non periodic in Paper I, two were found periodic in only 1 or 2 ASAS time segments, and one had only one literature determination. Our results are summarised in Table B.1.

Concerning the revised periods, the previous determinations reported in Paper I were either based on literature values (1 target), had inconsistent vsini/v_eq ratio (4 targets), or were beat periods detected in less than five time segments (5 targets), or detected in five or more segments (3 targets). Based on this result for the period revision of a few targets in Paper I, in the present work we decided to consider a rotation period to be well established (confirmed) if detected in five or more time segments or in fewer, but with an independent determination from the literature.

In the following we update the results presented in Paper I including new results based on Super WASP and on a more conservative period selection.

TW Hydrae We found SuperWASP data for eight targets in TW Hya and confirmed the rotation periods of four targets, and determined three new periods. However, only one out of the three newly periodic targets (TWA 20) is a confirmed TWA member, the other two having been rejected or needing to be confirmed. The rotation period of TWA 23, although detected in three out of five time segments, has a critical value close to the data 1-day observation sampling. Therefore, even if reported in this work, it needs additional observations to be confirmed, therefore, we classify it as uncertain. The data of TWA 3 were quite sparse to be suitable for a period search.

To summarise, we have so far derived confirmed periods for 15 out of 17 certain late-type members of TW Hya. Rotation periods of TWA 3A and TWA 3B are still unknown.

βPictoris Data for 13 β Pic targets are available in the SuperWASP database, five of which have been recently identified as β Pic members by Kiss et al. (2011). For seven targets we confirm the period determined in Paper I. For the other six we determined previously unknown period, five of them classified as confirmed, the other one (J01071194-1935359) as likely.

To summarise, we derived confirmed periods for 29 of the 37 late-type members of β Pic. For a further three stars we determined likely periods, whereas for only one star we have an uncertain period. The rotation periods of four stars still remain unknown.

Tucana/Horologium Data for 19 Tucana/Horologium targets are available in the SuperWASP database, two of which have been recently identified as Tucana/Horologium members by Kiss et al. (2011). For nine targets we confirm the rotation periods determined in Paper I. For one target (J01521830-5950168) we determined the previously unknown period that we classify as uncertain.We revised the period of HIP 21632, which was taken from the literature in Paper I and based on Hipparcos photometry, and the period of TYC 8852 0264 1 whose earlier determination led to inconsistent vsini/v_eq ratio. This star was excluded in Paper I from rotation period evolution analysis also because it is a rejected member. SuperWASP data of six targets were quite sparse and unsuited for period search. Data of HD 25402 were suited but did not allow any period detection.

To summarise, we derived confirmed periods for 22 of 29 late-type members of Tucana/Horologium. Two stars have rotation periods still to be confirmed. Rotation periods of five stars HIP 490 HIP 6856, TYC 8489 1155 1, AF Hor, and HIP 16853 are still unknown.

Columba Data for 12 Columba targets are available in the SuperWASP database. For four targets we confirm the rotation period determined in Paper I. For two targets we determined the previously unknown period that we classify as confirmed. We revised five rotation periods. The revised period of TYC 7100 2112 1 now gives consistent vsini/v_eq ratio. The other four revised periods were in Paper I either beat periods or detected in four or fewer time segments, whereas they are now well established. Data of HIP 25709 were too sparse to allow a period determination.

To summarise, we derived confirmed periods for 20 of 23 late-type members of Columba. TYC 6457 2731 1 and TYC 5346 132 1 still have unknown periods. The period of HIP 25709 is classified as likely.

Carina We did not find any SuperWASP data for the Carina late-type members. We derived confirmed periods for 14 of 21 late-type members. Four stars have the period classified as likely. The periods of TYC 8584 2682 1, HD107722 is still unknown. TYC 8586 2431 1 has period leading inconsistent vsini/v_eq ratio.

AB Doradus Data for 26 AB Doradus targets are available in the SuperWASP database, and for three targets we determined the previously unknown period (one classified as confirmed, and two as likely). For 11 targets we confirm the rotation period determined in Paper I. We revised six periods, and did not detect any periodicity of five stars although the timeseries are suitable for the period search. The observations of one target are too sparse for period search. The rotation period of HIP 116910 reported in Paper I revealed itself to be the beat period of the confirmed P = 1.787 d discovered in SuperWASP data. The periods of TYC 7059 1111 1 and TYC 7598 1488 1 reported in Paper I led to inconsistent vsini/v_eq ratio, whereas the updated period solved the inconsistency. The period of TYC 7064 0839 1, TYC 7605 1429 1, and TYC 7627 2190 1 reported in Paper I were detected in less than five time segments, whereas the new periods are classified as confirmed.

To summarise, we derived confirmed periods of 29 of 64 late-type members of AB Doradus. Twenty members have periods classified as likely. The rotation period of 15 members is still unknown.

In Figs. B.1–B.3 we plot the updated rotation period distributions in the young associations studied in Paper I, where the newly discovered and the revised rotation periods are plotted with squared and squared crossed symbols, respectively, whereas circled symbols represent the rotation periods of the new candidate members proposed by Kiss et al. (2011).

Similarly, in Fig. 6 we plot the updated distributions of light curve amplitudes versus rotation period in the young associations studied in Paper I.

We notice that both rotation periods and light curve amplitudes of the newly proposed members by Kiss et al. (2011) agree with the values of the other confirmed association members. This evidence gives further support to their assigned membership.

© ESO, 2011