Supercycle of WX Hyi


(vsnet-chat 79)

Stan Walker wrote:

> I saw your note about WX Hydri. Rather than it being more active lately 
> it seems to have reverted to the earlier behaviour patterns. We looked at 
> this star from Auckland years ago - I think about the mid-1970s - looking 
> for an orbital period using pep. At that time it seemed to be bright 
> almost more often than it was faint and weekly outbursts weren't unusual. 
> 
> Not too long ago (in the last couple of years) it was suggested that WX 
> Hydri had stopped having outbursts. I'm unsure whether this was normal or 
> super, or even when the supposed cessation occurred. Was this ever true?

What are the current and past supercycle lengths of WX Hyi? Ritter's CV catalogue lists typical recurrence times of normal- and superoutbursts as 14 and 140 days, respectively. As a northerner with no chance to watch the object, I have suspected WX Hyi is one of dwarf novae having the shortest supercycle lengths, thus close to ER UMa stars. Reading discussions things may not be that simple...

The northern prototype, SU UMa, at least once had a spell without outbursts at all. Might it not resemble WX Hyi?

Regards,
Taichi Kato

(vsnet-chat 84)

G'day Stan (and vsnet readers),

On 1997-02-10 astroman@voyager.co.nz said:

   >Fraser Farrell wrote:
   >> WX Hyi's frequency of outburst was about 2 or 3 times per month a
   >>few  years ago, and outbursts were typically less than 2 days long.
   >>Even its  superoutbursts lasted no more than a week.  Now it is
   >>going off more  frequently, and for longer maxima. Taichi Kato
   >>seems to be right in  suggesting WX Hyi is trying to join "The ER
   >UMa Club".

   >I saw your note about WX Hydri. Rather than it being more active
   >lately it seems to have reverted to the earlier behaviour patterns.
   >We looked at this star from Auckland years ago - I think about the
   >mid-1970s - looking for an orbital period using pep. At that time
   >it seemed to be bright almost more often than it was faint and
   >weekly outbursts weren't unusual.

Eric Harries-Harris confirms that...

   >Not too long ago (in the last couple of years) it was suggested
   >that WX Hydri had stopped having outbursts. I'm unsure whether this
   >was normal or super, or even when the supposed cessation occurred.
   >Was this ever true?

You may be thinking of WX _Ceti_. Our (incomplete) records of WX Hyi show outbursts almost every month since 1990. The VSS RASNZ Circulars show at least two outbursts every month for the last several years; but outbursts were shorter in the late 1980's - early 1990's.

   >In the normal outbursts we measured there was no pause at maximum -
   >decline began immediately as with several other southern UGSU stars
   >- although this may be difficult to pick visually. The supermaxima
   >had good superhumps at the start but they soon became rather messy.

WX Hyi does seem to stay at max for about a day in normal outbursts now. We didn't detect any superhumps (visually) in the last supermax; but the weather wasn't good for most of us.

Your note and the Circulars suggest we may be seeing a long-term periodic variation (~20 years??) in the behaviour of WX Hyi. If so, it may revert to lesser activity in about ten years or so.

I speculate that EG Cnc may represent an extreme example - decades of inactivity, then months (years??) of vigorous activity, then inactivity again. Perhaps this should be part of the definition of ER UMa stars? I await discussion from our professional readers!

cheers,

Fraser Farrell
Variable Stars Group
Astronomical Society of South Australia

WWW: http://www.gist.net.au/assa/   email: fraserf@dove.net.au
traditional:  GPO Box 199, Adelaide, SA 5001, Australia

(vsnet-chat 85)

Fraser Farrell wrote:

> I speculate that EG Cnc may represent an extreme example - decades of
> inactivity, then months (years??) of vigorous activity, then inactivity
> again.  Perhaps this should be part of the definition of ER UMa stars?
> I await discussion from our professional readers!
I believe the ER UMa stars are defined by their short supercycle lengths, and not by activity/inactivity cycles. ER UMa stars are assumed to have exceptionally high mass-transfer rates among SU UMa-type dwarf novae, in contrast to EG Cnc or WZ Sge-stars. However, it is still under investigation whether secular changes exist in ER UMa stars.

I hope Nogami-san has some comments on this matter.

Regards,
Taichi Kato

(vsnet-chat 87)

Taichi Kato wrote:

 > Fraser Farrell wrote:
 > > I speculate that EG Cnc may represent an extreme example - decades of
 > > inactivity, then months (years??) of vigorous activity, then inactivity
 > > again.  Perhaps this should be part of the definition of ER UMa stars?
 > > I await discussion from our professional readers!
 >     I believe the ER UMa stars are defined by their short supercycle
 > lengths, and not by activity/inactivity cycles.  ER UMa stars are assumed
 > to have exceptionally high mass-transfer rates among SU UMa-type dwarf
 > novae, in contrast to EG Cnc or WZ Sge-stars.  However, it is still
 > under investigation whether secular changes exist in ER UMa stars.

The original definitions of ER UMa stars given by Nogami et al. (1995, PASJ 47, 897) are: 1) the extremely short supercycle, 2) the extraordinary long duty cycle, 3) the normal outbursts repeating with a very short cycle length, and 4) the small amplitude of a superoutburst ($\sim3$ mag). All of these are concerned with CURRENT activities. However, the secular change of the activity and the mass transfer rate is one of the hottest topics in observational and theoretical studies of CVs. Close monitoring ER UMa stars (though RZ LMi and DI UMa might be too faint for visual observers) is highly encouraged!

As for EG Cnc, it is disappointing that the spectacular show seems to have ended (though EG Cnc has stayed slightly brighter than its genuin quiescence). However, an interesting problem is left: what's the mechanism for the show?

1) purely disk-originated phenomena
2) ER UMa-like behavior caused by temporarily enhanced mass transfer
      from the secondary star heated by the superoutburst
3) others

Which do you bet?

Regards,
Daisaku Nogami

(vsnet-chat 91)

G'day all,

On 1997-02-15 tkato@kusastro.kyoto-u.ac.jp said:

   >What are the current and past supercycle lengths of WX Hyi?
   >Ritter's CV catalogue lists typical recurrence times of normal- and
   >superoutbursts as 14 and 140 days, respectively.  As a northerner

Ritter's supercycle looks about right, but the normal cycle is now noticeably quicker than 14 days. In fact WX Hyi is now going off so frequently that my local observers no longer consider outbursts to be worth telephoning me about!

   >with no chance to watch the object, I have suspected WX Hyi is one
   >of dwarf novae having the shortest supercycle lengths, thus close
   >to ER UMa stars.  Reading discussions things may not be that simple.

I think there may be a continuum of possible CV systems, ranging from the ER UMa's (or even X-ray bursters?) through the "normal" UG's to the NR's and right out to the "hibernating" novae. However, our recognition of the rapid systems has been rather belated ( _V1159_ Ori??) and I'm sure there are more of them; misclassified in the GCVS.

Maybe if any of these systems was observed for several hundred/thousand outburst cycles; it might be discovered that all of them go through a very long period cycle of few/no outbursts and "frequent" outbursts??

Just speculating.... :)


cheers,

Fraser Farrell
Variable Stars Group
Astronomical Society of South Australia

WWW: http://www.gist.net.au/assa/   email: fraserf@dove.net.au
traditional:  GPO Box 199, Adelaide, SA 5001, Australia

(vsnet-chat 94)

On Sat, 15 Feb 1997, Taichi Kato wrote:

> Subject: [vsnet-chat 79] supercycle of WX Hyi?
> 
>     What are the current and past supercycle lengths of WX Hyi?  Ritter's
> CV catalogue lists typical recurrence times of normal- and superoutbursts
> as 14 and 140 days, respectively.  As a northerner with no chance to watch
> the object, I have suspected WX Hyi is one of dwarf novae having the shortest
> supercycle lengths, thus close to ER UMa stars.  Reading discussions things
> may not be that simple...

It is known that SU UMa stars change their supercycles (time length between superoutbursts) after a certain time (several supercycles or more), see Vogt (1980, Astronomy & Astrophysics 88, page 66). They usually change between 2 or 3 supercycle lengths. At that time was only, however one mean length known for WX Hyi: ~142 days. So, whether WX Hyi switches between different supercycles length would be an interesting question.

Erik Kuulkers

(vsnet-chat 95)

On Sun, 16 Feb 1997, Fraser Farrell wrote:

> Subject: [vsnet-chat 84] Re: EG Cnc - first one?

> I speculate that EG Cnc may represent an extreme example - decades of
> inactivity, then months (years??) of vigorous activity, then inactivity
> again.  Perhaps this should be part of the definition of ER UMa stars?
> I await discussion from our professional readers!

My understanding is that the ER UMa stars show much longer timescales of very frequent outbursting behaviour than the more than 2 months activity of EG Cnc. The ER UMa stars also show various supercycles after each other on short timescales, whereas the EG Cnc and systems alike (TOADs or WZ Sge stars) several short outbursts after a superoutburst and then nothing for a long time thereafter, i.e. they have very long supercycle times.

Erik Kuulkers

(vsnet-chat 97)

Fraser Farrell wrote:

> Ritter's supercycle looks about right, but the normal cycle is now
> noticeably quicker than 14 days.  In fact WX Hyi is now going off so
> frequently that my local observers no longer consider outbursts to be
> worth telephoning me about!

It's interesting to hear this particular star actually changes normal cycle length (or outburst frequency) without affecting the supercycle length, since theory predicts there should be a tight relation between the normal cycle length (Tn) and supercycle (Ts) with reasonable assumptions. (cf. Warner B. 1995, ApSS, 226, 187)

> I think there may be a continuum of possible CV systems, ranging from
> the ER UMa's (or even X-ray bursters?) through the "normal" UG's to the
> NR's and right out to the "hibernating" novae.  However, our recognition
> of the rapid systems has been rather belated ( _V1159_ Ori??) and I'm
> sure there are more of them; misclassified in the GCVS.

It is now widely believed ER UMa stars essentially obey the same outburst physics as usual SU UMa stars, but it is not known whether there is a continuous spectrum covering both ER UMa stars and usual SU UMa stars. Observationally there seems to be a gap in supercycle lengths between 45 days and 90 days. I hope Nogami-san especially working on this topic may have some comments (^_^).

> Maybe if any of these systems was observed for several hundred/thousand
> outburst cycles; it might be discovered that all of them go through a
> very long period cycle of few/no outbursts and "frequent" outbursts??

As Nogami-san pointed out in PASJ 47, 897 and in Keele CV Conference (and others?), it would be unlikely the present high activity of ER UMa stars should represent their secular average -- otherwise it would be difficult to explain the existence of extremely short Porb systems like DI UMa or RZ LMi within the widely accepted framework of CV evolution.

Even if secular interchanges between ER UMa stars and usual SU UMa stars (or even WZ Sge stars) may exist, it is not yet known whether the time of ER UMa stars' turning-off is earlier than the SN Betelgeuse or SN Eta Car ...

Regards,
Taichi Kato

(vsnet-chat 114)

G'day all,

On 1997-02-18 tkato@kusastro.kyoto-u.ac.jp said:

   >Fraser Farrell wrote:
   >> noticeably quicker than 14 days.  In fact WX Hyi is now going off
   >>so  frequently that my local observers no longer consider
   >>outbursts to be  worth telephoning me about!

   >It's interesting to hear this particular star actually changes
   >normal cycle length (or outburst frequency) without affecting the
   >supercycle length, since theory predicts there should be a tight
   >relation between the normal cycle length (Tn) and supercycle (Ts)
   >with reasonable assumptions. (cf. Warner B. 1995, ApSS, 226, 187)

I read that somewhere as well. But theory is derived from observation, so here's a summary of WX Hyi outbursts since 1995 October 9 (JD 2450000) from the VSS RASNZ Circulars:

JD 2450000+     max mag     rise-max-fall (days)
-----------     -------     --------------------
   004            12.0        0.8-1.4-0.6
   015            12.5        1.2-2.1-1.8
   024            11.9        1.0-0.0-3.3
   033            12.1        0.6-1.2-1.2
   045            11.7        0.8-1.0-2.0
   055            11.8        2.7-6.3-4.0 supermaximum
   070            12.4        1.0-0.2-1.0
   081            12.4        0.6-1.3-0.6
   087            12.8        1.0-0.6-0.4
   093            12.9        1.0-1.0-1.0
   100            12.8        0.3-0.0-0.4
   107            12.5        1.0-0.9-2.0
   114            12.6        1.0-
   123            12.8        0.9-1.0-1.0
   133            12.5        1.8-0.2-3.0
   142            12.4        1.0-
   155            12.4        1.0-1.0-1.0
   168            11.4        0.4-0.5-2.0
   181            11.5        1.0-0.0-1.0
   191            12.6        1.0-1.7-1.3
   206            11.2        3.0-5.6-3.0 supermaximum
   221            12.4        0.4-0.0-0.1
   226            12.5        1.0-1.0-1.0
     236-265 missing Circular (!)
   276            12.0        2.0-0.0-1.6
   292            12.2        0.8-1.0-1.0
   302            12.2        0.6-1.5-0.8
   314            12.2        0.8-0.0-1.2
   326            12.3        1.2-
   339            12.2        1.5-1.3-1.2
   350            12.7        1.0-0.8-0.5
   363            12.0        2.9-5.0-5.7 supermaximum (the odd one)
   380            12.5        1.1-0.0-0.9
   386            12.5        1.4-0.7-1.0
   394            12.4        1.2-0.2-2.3
   406            12.8        2.0-0.0-1.0
   416            12.0        1.8-1.0-1.1

The supermax intervals were 151 and 157 days. Detecting changes in the supercycle will take a few more years(!); but, assuming that all other outbursts are normal (not post-supermax hiccups) the mean cycle for this listing is 9.9 +/- 2.7 days (1 sigma). The mean normal outburst duration is 1.0-0.7-1.2 days, +/- 0.4-0.6-0.7 days.

WX Hyi is circumpolar for most VSS RASNZ observers, and under regular scrutiny from at least 8 experienced observers every month. I think every outburst in this time interval has been seen; and the cycle has definitely shortened from Ritter's result.

Are we looking at the prototype of the "WX Hyi variables" ??

cheers,

Fraser Farrell
Variable Stars Group
Astronomical Society of South Australia

WWW: http://www.gist.net.au/assa/   email: fraserf@dove.net.au
traditional:  GPO Box 199, Adelaide, SA 5001, Australia

(vsnet-chat 128)

After reading recent postings on the possible change in outburst behavior of WX Hyi, I have noticed in the GCVS 3rd the star was classified as a Mira star (10.7-14.2p). Some references show the "peculiar" blue color and rapid variation of this star were noted by Philip in IAUC 2348 and confirmed by subsequent authors including Sonneberg researchers (IBVS 578).

Is this a famous story?

Regards,
Taichi Kato


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