Revisiting the connection between magnetic activity, rotation period, and convective turnover time for main-sequence stars

The connection between stellar rotation, stellar activity, and convective turnover time is revisited with a focus on the sole contribution of magnetic activity to the Ca II H&K emission, the so-called excess flux, and its dimensionless indicator R$^{+}_{\rm{HK}}$ in relation to other stellar parameters and activity indicators. Our study is based on a sample of 169 main-sequence stars with directly measured Mount Wilson S-indices and rotation periods. The R$^{+}_{\rm{HK}}$ values are derived from the respective S-indices and related to the rotation periods in various $B-V$-colour intervals. First, we show that stars with vanishing magnetic activity, i.e. stars whose excess flux index R$^{+}_{\rm{HK}}$ approaches zero, have a well-defined, colour-dependent rotation period distribution; we also show that this rotation period distribution applies to large samples of cool stars for which rotation periods have recently become available. Second, we use empirical arguments to equate this rotation period distribution with the global convective turnover time, which is an approach that allows us to obtain clear relations between the magnetic activity related excess flux index R$^{+}_{\rm{HK}}$, rotation periods, and Rossby numbers. Third, we show that the activity versus Rossby number relations are very similar in the different activity indicators. As a consequence of our study, we emphasize that our Rossby number based on the global convective turnover time approaches but does not exceed unity even for entirely inactive stars. Furthermore, the rotation-activity relations might be universal for different activity indicators once the proper scalings are used.Comment: 13 pages, 7 figures, accepted for publication in A&

Psychophysiological correlates of peritraumatic dissociative responses in survivors of life-threatening cardiac events

The psychophysiological startle response pattern associated with peritraumatic dissociation (DISS) was studied in 103 survivors of a life-threatening cardiac event (mean age 61.0 years, SD 13.95). Mean time period since the cardiac event was 37 (79 IQD) months. All patients underwent a psychodiagnostic evaluation (including the Peritraumatic Dissociative Experiences Questionnaire) and a psychophysiological startle experience which comprised the delivery of 15 acoustic startle trials. Magnitude and habituation to trials were measured by means of electromyogram (EMG) and skin conductance responses (SCR). Thirty-two (31%) subjects were indexed as patients with a clinically significant level of DISS symptoms. High-level DISS was associated with a higher magnitude of SCR (ANOVA for repeated measures p = 0.017) and EMG (p = 0.055) and an impaired habituation (SCR slope p = 0.064; EMG slope p = 0.005) in comparison to subjects with no or low DISS. In a subgroup analysis, high-level DISS patients with severe post-traumatic stress disorder (PTSD; n = 11) in comparison to high-level DISS patients without subsequent PTSD (n = 19) exhibited higher EMG amplitudes during all trials (repeated measures analysis of variance IF = 5.511, p = 0.026). The results demonstrate exaggerated startle responses in SCR and EMG measures - an abnormal defensive response to high-intensity stimuli which indicates a steady state of increased arousal. DISS patients without PTSD exhibited balanced autonomic responses to the startle trials. DISS may, therefore, unfold malignant properties only in combination with persistent physiological hyperarousability. Copyright (C) 2002 S. Karger AG, Basel

Revisiting the cycle-rotation connection for late-type stars

We analyse the relation between the activity cycle length and the Rossby number and collected a sample of 44 main sequence stars with well-known activity cycle periods and rotation periods. We find a linear behaviour in the double-logarithmic relation between the Rossby number and cycle period. The bifurcation into a long and a short period branch is clearly real but it depends, empirically, on the colour index B-V, indicating a physical dependence on effective temperature and position on the main sequence. Furthermore, there is also a correlation between cycle length and convective turnover time with the relative depth of the convection zone. Based on this, we derive empirical relations between cycle period and Rossby number, and for the short period cycle branch relations, we estimate a scatter of the relative deviation between 14% and 28% on the long-period cycle branch. With these relations, we obtain a good match with the 10.3 yr period for the well known 11-year solar Schwabe cycle and a long-period branch value of 104 yr for the Gleissberg cycle of the Sun. Finally, we suggest that the cycles on the short-period branch appear to be generated in the deeper layers of the convective zone, while long-period branch cycles seem to be related to fewer deep layers in that zone. We show that for a broader B-V range, the Rossby number is a more suitable parameter for universal relation with cycle-rotation than just the rotation period alone. As proof, we demonstrate that our empirical stellar relations are consistent with the 11-year solar Schwabe cycle, in contrast to earlier studies using just the rotation period in their relations. Previous studies have tried to explain the cycle position of the Sun in the cycle-rotation presentation via other kinds of dynamo, however, in our study, no evidence is found that would suggest another type of dynamo for the Sun and other stars.Comment: 18 pages, 18 figures, accepted for publication in A&