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[vsnet-rcb 13] R CrB-type discussion from vsnet-chat
- Date: Sun, 2 Jul 2000 13:41:58 +0900 (JST)
- To: vsnet-rcb
- From: Taichi Kato <tkato>
- Subject: [vsnet-rcb 13] R CrB-type discussion from vsnet-chat
- Sender: owner-vsnet-rcb@kusastro.kyoto-u.ac.jp
R CrB-type discussion from vsnet-chat
This thread in vsnet-chat may be of interest to new readers of vsnet-rcb.
Subject: [vsnet-chat 2968] RE: [vsnet 2012] EsB365 observations and request
Thanks, Brian.
The BAA VSS lists EsB365 as a probable RCB type and ranging between 8.9 and
10.8.
Comparing BAA data with AAVSO (The new light curve generator is online
beginning today) I see that observations are quite the same. The first
section of the curve is made up with the same points and the more recent
ones ( in AAVSO) are all mine.
I encourage observers on observing this star. Come on, Southern skywatchers,
this is a good one, its colour makes it a challenge and it's very easy to
find.
Regards,
Sebasti疣.
Subject: [vsnet-chat 2970] Re: [vsnet 2012] EsB365 observations and request
Sebastian Otero wrote:
> Thanks, Brian.
> The BAA VSS lists EsB365 as a probable RCB type and ranging between 8.9 and
> 10.8.
> Comparing BAA data with AAVSO (The new light curve generator is online
> beginning today) I see that observations are quite the same. The first
> section of the curve is made up with the same points and the more recent
> ones ( in AAVSO) are all mine.
> I encourage observers on observing this star. Come on, Southern skywatchers,
> this is a good one, its colour makes it a challenge and it's very easy to
> find.
> Regards,
> Sebastin.
Dear Sebastian and VSNet folks,
I have updated the EsB365 lightcurve on the BAAVSS pages;
http://vsnet.telf-ast.demon.co.uk/gifm/00757a.gif
This now shows 57 estimates by Berto Monard as contributed to The Astronomer
magazine and the BAAVSS.
Berto reports to us mainly on Southern RCB's, which is why I originally
listed it as a suspected one.
Probably other suggested tentative types would be more appropriate?
Regards,
Dave
--
Dave McAdam dave@telf-ast.demon.co.uk
BAAVSS Secretary http://vsnet.telf-ast.demon.co.uk/
Subject: [vsnet-chat 2971] Re: [vsnet 2012] EsB365 observations and request
Although Es.-B. 365 could go through dimming episodes like V Hya, for
instance, RCB stars are more typically rather hotter (G type), and are not
red outside of these events. This star of course is an extremely red carbon
star, and is most likely to be either a slow variable of modest amplitude
(Lb in GCVS parlance) or perhaps a semiregular. Feel free (even encouraged)
to prove me wrong!
\Brian
Subject: [vsnet-chat 2972] RE: [vsnet 2012] EsB365 observations and request
Dear Dave:
Thanks for the update and your interest.
Brian Fraser from South Africa is also planning to observe this star.
I suggested an L type classification because of the lack (at least visually)
of cepheid-like pulsations and the slow developement of the light curve. The
main problem, of course, is the difference in colour with every other star.
We need to keep observing in order to catch some fading but I think that the
amplitude of the light curve is due to systematic differences between
observers rather than RCB behaviour.
The last couple of months I haven't seen any variations.
Feel free to use the observations I presented in vsnet-obs 27859.
Regards,
Sebasti疣 Otero, Buenos Aires,
Argentina.
Subject: [vsnet-chat 2973] RE: [vsnet 2012] EsB365 observations and request
Sebastian Otero wrote:
> Dear Dave:
> Thanks for the update and your interest.
> Brian Fraser from South Africa is also planning to observe this star.
> I suggested an L type classification because of the lack (at least visual=
ly)
> of cepheid-like pulsations and the slow developement of the light curve. =
The
> main problem, of course, is the difference in colour with every other sta=
r.
> We need to keep observing in order to catch some fading but I think that =
the
> amplitude of the light curve is due to systematic differences between
> observers rather than RCB behaviour.
> The last couple of months I haven't seen any variations.
> Feel free to use the observations I presented in vsnet-obs 27859.
> Regards,
> Sebasti=E1n Otero, Buenos Aires,
> Argentina.
Thanks Sebastian, I shall place your observations in our database and
amend the type to 'L?'.
Further monitoring by several observers should show up systematic differenc=
es
more clearly, (if these really are a factor) and another fade like the one
in Jan-Feb 1998 could occur.
Best Regards,
Dave
--
Dave McAdam dave@telf-ast.demon.co.uk
BAAVSS Secretary http://vsnet.telf-ast.demon.co.uk/
Subject: [vsnet-chat 2978] RE: [vsnet 2012] EsB365 observations and request
> Although Es.-B. 365 could go through dimming episodes like V Hya, for
> instance, RCB stars are more typically rather hotter (G type), and are not
> red outside of these events. This star of course is an extremely red
carbon
> star, and is most likely to be either a slow variable of modest amplitude
> (Lb in GCVS parlance) or perhaps a semiregular. Feel free (even
encouraged)
> to prove me wrong!
>
> \Brian
I totally agree with you about the classification and the color comments.
RCB's are supergiants supposedly created from the coalescence of two white
dwarfs and very red carbon stars are red giants, so I don't think this one
is an RCB. But let me tell you that I won't feel sad if it decides to fades
8 magnitudes some day...
Subject: [vsnet-chat 2979] Re: EsB365 observations and request
> Although Es.-B. 365 could go through dimming episodes like V Hya, for
> instance, RCB stars are more typically rather hotter (G type), and are not
> red outside of these events. This star of course is an extremely red
carbon
> star, and is most likely to be either a slow variable of modest amplitude
> (Lb in GCVS parlance) or perhaps a semiregular. Feel free (even encouraged)
> to prove me wrong!
>
> \Brian
DY Per is probably a problematic case. This star, usually considered
as an R CrB star, is a cool carbon stat having B-V=2.55 at V=12.60 (Henden).
Hotter R CrB stars also exist, such as MV Sgr, another relatively overlooked
object.
Regards,
Taichi Kato
Subject: [vsnet-chat 2980] Re:EsB365 observations and request
Dear Dr.Kato,
the origin of the R CrB type stars is not clear up to the end.
The cases of DY Per, SV Sge, Z Umi, etc will change a view on this
matter.
The dimming is the widespread phenomenon, some of novae at the transition,
for example.
Therefore any observations are necessary ti decide this problem.
Regards,
Alexander Rosenbush
Dr.Kato wrote:
> DY Per is probably a problematic case. This star, usually considered
>as an R CrB star, is a cool carbon stat having B-V=2.55 at V=12.60 (Henden).
>Hotter R CrB stars also exist, such as MV Sgr, another relatively overlooked
>object.
Subject: [vsnet-chat 2982] RE: [vsnet 2012] EsB365 observations and request
Surely there are some more uncertain classifications, EsB365 not being the =
only one.=20
For instance V1860 Sgr is also considered a possible RCB and V803 Cen has =
been as well not so long ago.=20
B-V measures ought to sort most of them out....
Isn't the L* classification meant for those uncertain cases?=20
Regards,
Berto Monard
Subject: [vsnet-chat 2984] Cool R CrB stars?
Cool R CrB stars?
Further to add, some LMC carbon stars discovered by the MACHO collaboration
team show light curves quite similar to that of DY Per. The MACHO team
explained the light curve by the combination of superimposed periodicity.
Some carbon Mira stars are known to show episoding fading, presumably
caused by dust condensation. The best known example, followed by optical-IR
observations, may be R For. One of the northern star, V366 Lac = AFGL 2881,
originally discovered as a carbon Mira star, faded dramatically. This
object has been observed sporadically by a number of observers, but never
detected positivity. Could this be interpreted as M+RCB?
Regards,
Taichi Kato
Subject: [vsnet-chat 2985] Re: EsB365 observations and request
Re: EsB365 observations and request
Berto Monard wrote:
> For instance V1860 Sgr is also considered a possible RCB and V803 Cen has
> been as well not so long ago.
V1860 Sgr is not presently considered as an R CrB star based on
spectroscopy (see a list in Clayton 1996, PASP 108, 225). The key
discriminating factor is the hydrogen deficiency.
Yet another historically confusing group was the VY Scl-type CV. The
prototype VY Scl was originally discovered as a "blue, high galactic
lattitude" R CrB star. The author of the discovery paper keenly suggested
that there should be two polulations of R CrB stars.
Regards,
Taichi Kato
Subject: [vsnet-chat 2986] RE: [vsnet 2012] EsB365 observations and request
The L type is asigned to slow pulsating red stars and not to every star with
an uncertain classification. The * symbol is used for them. EsB365 is not
showing signs of eruptive variability and I agree with Brian Skiff in that
maybe it is an SR. But it is not showing any periodicity.
I have a long list of suspected and ex-suspected RCB's and I'm constantly
observing LV TrA, given as RCB: in the GCVS. But you can't be too confident
in classifications: Taking a look at The 75th Name List of Variable Stars
with the new GCVS designated stars, we can find ZETA PUPPIS, an O5Iaf
supergiant classified as a BY: , when BY's are defined as dwarfs of dKe and
dMe spectral type.
Let's keep on observing and we'll find out.
Regards,
Sebasti疣 Otero.
Subject: [vsnet-chat 2988] Re: R CrB stars
Re: R CrB stars
There has been also a suggestion that some deep minima of RVB stars
may be related to fadings of R CrB stars. Some authors (which I can't
recall) even claimed that U Aqr may be an RVB star. The recent deep
fading of RZ Vul may be also suggestive.
Regards,
Taichi Kato
Subject: [vsnet-chat 2989] Re: EsB365, R CrB stars
Very usefull discussion!
There are not R Cor Bor type stars.
There are stars with the R CrB type variablity!
my best wishes for all,
Alexander Rosenbush
Subject: [vsnet-chat 2990] to vsnet-chat 2982
Dear Friends,
let me make some addition to my previous
message (vsnet 2982).
In order to sound no proofless I am citing
- Gonzalez G. et al., 1998, ApJ Suppl., v114, N1, p133-149 with
one note (!) about 'morphological group'.
- Rosenbush A., Hydrogen-Deficient stars. ASP Conf.Ser. v.96, p91, 1996.
regards,
Alexander
Subject: [vsnet-chat 2991] Re: R CrB stars
Re: R CrB stars
> There are not R Cor Bor type stars.
> There are stars with the R CrB type variablity!
Whether it will be adequate or not to call sudden fadings caused by
dust formation as the R CrB type variablity, this process has been widely
observed in different sort of objects (R CrB stars themselves, carbon stars,
RVB minimum (possible), DQ Her-type novae etc.).
However, the population of R CrB stars definitely exists, sharing some
common characterstics (see Clayton's review). It is not clear whether
this class of variable represents a single or multiple classes of objects
(e.g. in evolution), or whether the class has a definite borderline between
R CrB stars and other variable stars.
Regards,
Taichi Kato
Subject: [vsnet-chat 2993] Re: R CrB stars
I think this we have to do with the variability spread
among definite class of objects: high mass loss rate;
enough high hydrogen (not very deficient!
FG Sge, V854 Cen, V CrA);
rich carbon.
They are evolved stars.
And this is no the single population (for example, Trimble V., Kundu A.,
PASP, 109, 1089, 1998).
Alexander Rosenbush
Subject: [vsnet-chat 2995] RE: R CrB stars
----- Original Message -----
From: Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>
To: <vsnet-chat@kusastro.kyoto-u.ac.jp>
Sent: Sunday, May 28, 2000 9:56 AM
Subject: [vsnet-chat 2991] Re: R CrB stars
> Whether it will be adequate or not to call sudden fadings caused by
> dust formation as the R CrB type variablity, this process has been widely
> observed in different sort of objects (R CrB stars themselves, carbon
stars,
> RVB minimum (possible), DQ Her-type novae etc.).
>
> However, the population of R CrB stars definitely exists, sharing some
> common characterstics (see Clayton's review). It is not clear whether
> this class of variable represents a single or multiple classes of objects
> (e.g. in evolution), or whether the class has a definite borderline
between
> R CrB stars and other variable stars.
>
> Regards,
> Taichi Kato
It seems to be at least two main kinds of RCB behaviour: the RCB that fall
from grace and the one-time performers. V366 Lac faded deeply but there is
another star I can't recall now that also "dissapeared" from the sky. And we
have V4334 Sgr, Sakurai's Object, that appeared suddenly and vanished
showing RCB behaviour but with too great amplitude. Or we have FG Sge, that
has changed its spectrum from B to K. Are we observing examples of real time
evolution? May a star go through this evolutinary phase that fast? And if
they are really examples of RCB, why do other stars spend more time behaving
like that?
Best regards,
Sebastian Otero.
Subject: [vsnet-chat 2997] Re: R CrB variability
>It seems to be at least two main kinds of RCB behaviour: the RCB that fall
>from grace and the one-time performers. V366 Lac faded deeply but there is
>another star I can't recall now that also "dissapeared" from the sky. And we
>have V4334 Sgr, Sakurai's Object, that appeared suddenly and vanished
>showing RCB behaviour but with too great amplitude. Or we have FG Sge, that
>has changed its spectrum from B to K. Are we observing examples of real time
>evolution? May a star go through this evolutinary phase that fast? And if
>they are really examples of RCB, why do other stars spend more time behaving
>like that?
In any case the evolutionary stage with the R CrB type variability is
very short-term. FG Sge quickly changes some of its variability parameters:
the last deep minimum was once and lasted one pulsation period! It "grazes"
this stage?
UV Cas before our eyes finished this variability in the beginning of
the XX century.
The mass of similar stars is low, therefore the mass layers with one
abundance are very thin.
And V4334 Sgr (Sakurai's Object) is the unique example,
and I think very slow nova.
(Or it is the bridge between the novae and the planetary nebulae.)
It is quite possible there is very small group (one population)
of classical R CrB (R CrB itself, RY Sgr, SU Tau and one-two more) stars.
Only now we accumulate knowledge on these unique objects
from visual (in the first turn), infrared, UV, spectral, polarimetry,
theoretic..
Previously one identificated the R CrB stars on their deep minima.
and now it can make on rather shallow minima but very typical shape.
My best wishes,
clear sky to all,
Alexander Rosenbush
vsnet-adm@kusastro.kyoto-u.ac.jp
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