All Tables

Table 1: The journal of ROSAT X-ray observations.
Table 2: Number of detected X-ray sources. For the definition of the energy bands see text.
Table 7: Final list of X-ray sources identified with stars attributed to cluster NGC 2451 A, yielding Williams number (W #), mean X-ray positions (J2000), offset ( $\Delta$ ) between X-ray and optical positions in arcsec, V magnitudes, measured B-V and de-reddened (B-V)₀ colour indices. An asterisk indicates values from the literature used for bright stars that are overexposed in our images. Where significant variations in the X-ray flux have been found an X is written into the Var column. Spectral types are given in parentheses if estimated from the colour index. The last column gives a common star designation.
Table 8: Same as Table 7, but for cluster NGC 2451 B.
Table 9: Same as Table 7, but for faint stars probably members of either of the two cluster, yet not known to which because of large errors in B-V. For the calculation of bolometric fluxes dependent on apparent magnitude and de-reddened colour, we assumed an average reddening of E(B-V) = 0.05.
Table 10: Same as Table 7, but for stars supposed to be non-members of the two NGC 2451 clusters. We assumed a reddening of 0.00 for stars to the right of the two cluster main sequences, 0.05 between the main sequences (X159, X182), and 0.10 to the left of the main sequences.
Table 11: Cross-check of membership derived for NGC 2451 A by Platais et al. (2001) and by our X-ray investigation.
Table 12: Probable late-type cluster members based on proper motion (Platais et al. 2001) that were not detected in X-rays.
Table 13: Best fit parameters for different isochrone fits to our observed NGC 2451 colour-magnitude diagrams. Yale g and l denote two different colour transformations (Green et al. 1987 and Lejeune et al. 1997), respectively.
Table 14: Characteristic data of the four X-ray flares that occurred during PSPC pointing A. Given are the decay time, the peak X-ray luminosity at the observed maximum, and the whole released energy in the X-ray range integrated over the observed time of the flare.
Table 15: Comparison of mean and median X-ray luminosities for NGC 2451 A and B and other clusters of similar age, i.e., $\alpha$ Per and Pleiades (Prosser et al. 1996) and NGC 6475 (Prosser et al. 1995). The log $L_{\rm x}$ values are given separately for F-type stars ( $0.31\le (B-V)_0<0.59$ ), G-type stars ( $0.59\le (B-V)_0<0.82$ ), K-type stars ( $0.82\le (B-V)_0<1.41$ ), and M-type stars ( (B-V)₀>1.41). The values in parentheses indicate the number of stars used. Note that in the case of NGC 6475 the colour intervals are slightly different and that the K-type stars are divided into early types (upper values) and late types (lower values).
Table 3: X-ray sources detected in PSPC pointing A. The first column lists a unique source number that is also used in the following Tables 4-6 and 7-10. CR is the count rate (in s^-1), ECR the corresponding error, hr is the hardness ratio (see text), $f_{\rm x}$ is the X-ray flux in 10^-13 erg cm^-2 s^-1, and $L_{\rm x}$ is the X-ray luminosity in 10³⁰ erg s^-1, given only if the distance (i.e., probable cluster membership, see Sect. 5) is known. The last column indicates whether a source is detected in the soft (s) or hard (h) passband only.
Table 4: Same as Table 3, but for PSPC pointing B.
Table 5: Same as Table 3, but for sources only detected in the pointing C, i.e., the merged pointings A and B.
Table 6: Same as Table 3, but for the HRI pointing H. Note that the HRI has no energy resolution, thus a hardness ration cannot be derived. UV in the last column indicates that a significant fraction of the HRI count rate may come from stellar UV radiation.