As has been seen1, the variability of some suspected variables has been confirmed by the Hipparcos results. What about the variables that were already "known". Did Hipparcos confirm their variability and periods ?
The following table shows a number of variables sorted according the the amount of variation detected and compares the periods found by Hipparcos with the GCVS data. n/a indicates that there was no entry for the variable in the Hipparcos Variability Annex. Periods are in days.
Variable HIP Hp scatter HIP GCVS data period period type IS Gem 32740 0.01 n/a 47 SRc VW Dra 84496 0.02 n/a 170 SRd d Ser 90441 0.03 n/a - I: RX Cep 3905 0.03 n/a 55 SRd BU Tau 17851 0.04 - - GCas SW CrB 76791 0.05 n/a 100 SRb V377 Cas 1543 0.05 n/a 0.030 DSct BN Gem 37074 0.06 - - GCas AB Aur 22910 0.06 - - Ina W Boo 71955 0.09 35.33 450 SRb XX Cam 19340 0.10 26 ? - RCB Beta Per 14576 0.14 - 2.8673043 EA/SD RW Cep 110504 0.16 - 346 SRd Rho Cas 117863 0.18 - 320 SRd Rho Per 14354 0.20 7.45 ?, 26.6 ? 50 SRb TU CVn 63024 0.25 - 50 SRb RR UMi 73199 0.26 1.5082 ? 43.3 SRb TV UMa 57362 0.38 125 ? 42 SRb BK Vir 61022 0.39 150 ? 150 SRb AG Peg 107848 0.47 - - Nc g Her 80704 0.48 - 89.2 SRb RX Boo 70401 0.51 - 340 SRb R CrB 77442 0.56 - - RCB SW Vir 64569 0.65 153.6 150 SRb SX Her 78994 0.74 206 ? 102.9 SRd CH Cyg 95413 0.78 - - ZAnd/SR U Del 102440 0.83 - 110 SRb W Cyg 106642 0.85 132.0 131.1 SRb Beta Lyr 92420 0.93 12.940 12.913834 EB AC Her 90697 1.07 75.30 75.01 RVa RZ Cas 13133 1.10 1.195250 1.195247 EA/SD R Sct 92202 1.17 - 146.5 RVa Z UMa 58225 1.19 202.0 195.5 SRb V CVn 65006 1.39 191.5 191.89 SRa U Ori 28041 3.43 367 368.3 Mira RW Tau 18792 >3.80 2.76884 2.7688356 EA/SD R UMa 52546 4.32 299.7 301.62 Mira Chi Cyg 97627 5.19 402.3 408.05 Mira
Although the Hp photometric measures are not exactly the same as visual magnitudes, their scatter does give a good approximation as to the amount of variation seen in each variable by Hipparcos.
For some variables the amount of variation was clearly small - comparable with that seen for the less convincing suspected variables. Note also that the Mira variables will have faded below the detection limit at times.
The agreement on periods tends to be good for Mira type and eclipsing variables. For some semi-regular variables their is good agreement between the Hipparcos and GCVS values ; for others there is not. Hipparcos was able to detect short period and/or low amplitude variations in these variables more readily than can be done from visual estimates. The possible 26 day period in XX Cam is notable.
On the other hand, the 3 year mission duration and the limited number of measurements per star did make it difficult to detect longer periods or multiple periodicities. The limited number of measurements can also lead to minima being missed. This probably explains the failure to detect the periodicity in Beta Per and R Sct. Similarly, R CrB and AB Aur would have had larger ranges of Hp measures if sampled in other years.
Hence, although the Hipparcos data do provide some answers, there is still a lot of work for amateurs to do.
1 Suspected Binocular Variables in the Hipparcos data