IPs

AE Aqr
FO Aqr
XY Ari
V405 Aur
HT Cam
MU Cam
DW Cnc
BG CMi
V709 Cas
V1025 Cen
TV Col
TX Col
UU Col
V2306 Cyg
YY Dra
PQ Gem
DQ Her
EX Hya
NY Lup
V2400 Oph
GK Per
AO Psc
WX Pyx
V1223 Sgr
V1062 Tau
EI UMa
IGR 00234
IGR 15094
IGR 17303
Swift J0732
RX J0704
RX J1803
RX J2133
XSS 00564

Full Catalog

Related Systems

The Spin Period: Ups and Downs

Long-term tracking of the spin period is equally important, for several reasons.

• At a pragmatic level, when we obtain, e.g., new X-ray data, we want to be able to phase it to a known spin ephemeris.
• The relative stability of the spin period is an evidence for the white dwarf, as opposed to neutron star, nature of the compact object.
• One can deduce the magnetic moment of the white dwarf if we assume that IPs are at or near their long-term spin equilibrium. This assumption needs to be confirmed, however. Patterson (1994) predicts that Pdot of IPs in spin equilibrium will not be steady.
• Observational determiation of spin up/down gives a better handle on the magnetic moment, and hence allows an observational test of spin equilbrium (Patterson 1994). We might also be able to deduce something about the degree of departure from secular mean accretion rate in these systems.

Notes on Inidividual Systems

1. Systems which have shown a complex spin history
   • FO Aqr: Patterson et al (1998) present the most recent spin ephemeris. Both quadratic and cubic terms are necessary (the star was spinning down in the early to mid 1980s, then swithced to spin up in more recent years). Despite the long baseline, extrapolation of ephemeris is unlikely to be reliable, and in fact Williams (2003) was unable to establish a unique ephemeris through 2002. FO Aqr is almost certainly near spin equilibrium, and "we are fitting noise" in the period history. CBA continues to monitor this star extensively, which is reflected in the archive.
   • EX Hya: Mauche et al. (2009) contains the most recent published spin ephemeris, according to which this system shows a secular spin-up, but a cubic term is needed for. a good fit. More data are available at the CBA archive
2. Systems which have shown a secular spin-up
   • BG CMi: A steady spin-up is seen over 15 years; see Hellier (1997a) for details. Further monitoring would be desirable to see if the Pdot is constant or not, since there is a slight difference between the value derived by Hellier (1997a) and that in Patterson & Thomas (1993). This is another regular target of the CBA network.
   • DQ Her: Zhang et al. (1959) compiled the spin timings over 40 years and conclude that a cubic ephemeris is necessary. As of 1967, Pdot was -6.4x10^-13 but it will go to zero in about 70 years. The CBA archive mostly contains fast photometry at MDM.
   • GK Per: Secular spin-up was inferred for this source using a mixture of X-ray and U-band data by Patterson (1991), but with cycle count uncertainties. Recently, Mauche (2004) has made a secure determination of the spin-up rate using X-ray data alone. In the optical, U-band observations appear to be essential for a secure detection of the spin signal. Some data (in U and other bands) exist in the CBA archive.
   • AO Psc: Williams (2003) has confirmed the secular spin-up of this system, but was unable to provide a unique ephemeris. There is also an extensive set of data in the CBA archive.
3. Systems which have shown a secular spin-down
   • AE Aqr: Based on about 15 years of spin timing data, de Jager et al (1994) has derived a steady spin-down at the rate of Pdot(33s)=5.642(20)x10^-14 d d^-1. This is one important supporting evidence for the propeller model for this system. The ephemeris is very precise, but continued monitoring is highly desirable to confirm if the spin-down is really constant. There are no data at the CBA, presumably because the spin period of AE Aqr is too short for the network.
   • PQ Gem: A steady spin-down is seen over ~10 years; see Evans, Hellier & Ramsay (2006) for details. There are a lot of monitoring data by the CBA network over the last couple of years.
   • V1223 Sgr: A secular spin-down was inferred by Jablonski & Steiner (1987) based on the sideband period ephemeris. The true spin period is reliably seen in X-rays but rarely? (ever?) seen in the optical, and there is no long-term spin ephemeris. This star then became almost forgotten, but there are plenty of data in the CBA archive since 2000.
4. Systems for which spin up/down has not been measured
   • HT Cam: Based on CBA observations during 1997-2002, Kemp et al (2002) have derived a very precise linear ephemeris, with a shelf life of over 30 years. They've established an upper limit on Pdot of 2x10^-11.
5. Systems for which a good ephemeris is not yet available
   • XY Ari: The spin period was determined to be 206.3 +/- 0.1 s by Koyama et al (1991) using Ginga X-ray data. Subsequent X-ray and IR data only confirmed this value. Given the lack of an optical counterpart, it would be very difficult to do much better.
   • V405 Aur: The spin ephemeris of Skillman (1996) has a nominal shelf life of 36 years; however, if we instead take the difference in period between this ephemeris and that of Allan et al (1996) as the true uncertainty, the shelf life drops to 10 years. In any case, CBA observers have kept a close eye on this source in recent years.
   • V709 Cas: Kozhevnikov (2001) have observed this star during 1999 Oct 4-9 and detected the spin modulation at 312.77 +/- 0.04 s; the implied ephemeris has a 28.3 day shelf life. There are many datasets in the CBA archive.
   • V1025 Cen: Buckley et al (1998) finds 2146.59 s spin period from photometry in 1995 and 1996. There are a couple of datasets archived at the CBA.
   • TV Col: I am not aware of any spin ephemeris for this system. The spin is primarily seen in X-rays, mostly with insufficient duration to establish an ephemeris. The only mention of positive detection of this period in the optical I've seen is in the "note added in proof" of Bonnet-Bidaud, Motch & Mouchet (1985).
   • TX Col: Spin period inferred from X-ray and optical data (1984-1985) is 1911 +/- 2 s (Buckley & Tuohy (1989). Spin period is weakly seen in the optical, and various sidebands come and makes it difficult (if not impossible) to establish a long term ephemeris for this system. An extensive CBA campaign was carried out in Jan-Feb 2002.
   • UU Col: Burwitz et al (1996) conclude that the probable spin period is 863.5 +/- 0.7 s from 4 nights of data during 1996 January 13-17. Shelf life of the implied ephemeris is 12 days. No data have been archived at CBA as of 2003 April 14.
   • V2306 Cyg: The Norton et al (2002) ephemeris for half-spin period is based on 7 nights of V-band photometry at JKT, 2000 July 9-15. Shelf life of the implied ephemeris is 180 days. The amount of data at CBA is very low, probably because of the crowded field.
   • YY Dra: Table 6 of Haswell et al (1997) contains the most up-to-date table that I know of of the spin period, determined from X-ray and/or U band photometry (usually via its 1st harmonic). Data spanning many years are combined yet the uncertainty is such that the implied shelf life of the ephemeris is only 6 months. The lack of strong signal in white light photometry makes it difficult to establish a long-term ephemeris.
   • V2400 Oph: Buckley et al (1995) and Buckley et al (1997) have identified 927.66 +/- 0.41 s spin period from polarimetry and 1003.299 +/- 0.003 s synodic period from photometry during 1991-1994. However, 1027 s period was also possible from these data. Assuming the 1003 s period, the implied ephemeris has a shelf life of 10 years. One campiang on this star in 2001 June and July is archived at CBA.
   • V1062 Tau: Remillard et al (1994) derived a period of 1.054+/-0.005 hr = 3794 +/- 18 s from 4 nights of I-band data, whereas Hellir, Berdmore & Mukai (2002) derived 3704 +/- 8 s from 2 days of (ASCA and RXTE) X-ray observations. More data are needed to establish the spin period. Some data exist at CBA, particularly during 2002 December.
   • NY Lup: Haberl, Motch & Zickgraf (2002) observed this object from ESO on three consecutive nights, 1998 May 7-9. Shelf life of the implied ephemeris is 10 days. No data have been archived at CBA as of 2003 April 14.