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Eyepiece Views: January, 2006
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THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
25 Birch Street, Cambridge, MA 02138 USA
Tel. 617-354-0484 Fax 617-354-0665
http://www.aavso.org
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E Y E P I E C E V I E W S #312
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January, 2006
Table of Contents
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1. Introduction
2. Observing Variable Stars with Binoculars
From AAVSO Visual Observing Workshops, Fall 2005
3. The Story of a Variable Star Observation - The Magic of Web Obs
From AAVSO Visual Observing Workshops, Fall 2005
4. Star Partying 101
5. CV Comments
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1. INTRODUCTION - Best wishes for the year ahead and always!
As promised in the previous issue of Eyepiece Views, we continued to include
talks in this one from the Visual Observing Workshop conducted at the annual
fall meeting, held in Newton, MA on October 14-15 2005.
You will enjoy reading "Observing Variable Stars with Binoculars" from our
president David Williams while "The Story of a Variable Star Observation" by
Glen Chaple will take you through a single observation's journey from
submission on.
"Star Partying 101" is a lively piece which is an unedited version of Haldun
Menali's talk presented at one of his Toastmasters' meetings towards science
teachers, students who are also amateur astronomers and general public. Our
finale is spectacular, as always, with a piece from our avid contributor Mike
Simonsen. Our pieces are both educational and fun to read which is what we
think is making our publication worthwhile to read.
Now sit back, relax and enjoy the ride!
We wish you a wonderful 2006 ahead with the best dark, clear skies.
Thanks and good observing!
Gamze Menali, AAVSO Technical Assistant (MGQ)
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2. OBSERVING VARIABLE STARS WITH BINOCULARS - David B. Williams
The meaning of the word binocular says it all: two eyes. There are two
types of binoculars, field glasses and prismatic binoculars. Field glasses
(and the low-power version, opera glasses) are "straight-through" optical
systems with only objectives and eyepieces. Prismatic binoculars include a
set of prisms that fold the light path between the objectives and eyepieces,
creating a more compact optical system.
My first optical instrument was a pair of 6x30 binoculars. These revealed
many Messier objects and I also used them to make my first variable star
estimates. Many amateurs begin with binoculars, because they are often
available in the household when the initial interest in astronomy is born.
The Sky and Telescope web site has a feature titled "Binoculars, Halfway to
a Telescope." This is a calumny, because binoculars are actually twice a
telescope! Binoculars aren't second-choice substitutes for "real"
telescopes, they are simply small telescopes.
What's good about binoculars? They are small, eliminating considerations of
storage and transportation. And they can be put to use quickly – no set-up
time! When the temperature is far below freezing, I can step outdoors with
my binoculars and make several estimates of familiar variables and jump back
indoors in less than five minutes.
Binoculars are inexpensive. Reasonably good binoculars can be purchased for
just a few dollars on eBay (I bought my secondhand 7x35s for $17). They are
multi-use instruments that can be used for sports and nature viewing as well
as astronomy. And binoculars are wide-field, erect-image instruments,
making it easy to find your way around the night sky.
What's bad about binoculars? Not much. They have small apertures and low
magnifications, but these characteristics are also advantages when you are
observing bright variables and need a wide field of view.
Best of all, binoculars let you use both eyes! Since the evolutionary
development of the eye 600 million years ago, vision has been based on the
combination of two visual signals. Your brain is wired to process two
visual channels, enhancing resolution and contrast. When you think about
it, looking at anything with just one eye is a very strange thing to do.
Monocular telescope users are sometimes advised to keep both eyes open,
covering one with a hand or eye patch, to relieve the deficiencies of
viewing with just one eye.
Binoculars are designated by their magnifying power and their aperture in
millimeters. Thus, my first pair of 6x30 binoculars provided a magnifying
power of 6 with an aperture of 30 mm. Most binoculars come in
power-aperture ratios of 1:5 (6x30, 7x35, 10x50) or 1:7 (7x50, 9x63, 11x70).
Dividing the aperture of binoculars in millimeters by the magnification
gives you the diameter of the optical system's exit pupil. Thus, 1:5 ratio
binoculars produce an exit pupil of about 5 mm, while the 1:7 ratio produces
an exit pupil of about 7 mm. The maximum aperture of the dark-adapted human
eye is about 8 mm, which shrinks with advancing age (that's why children can
usually see fainter stars with the unaided eye than adults, another example
of how youth is wasted on the young). Their larger exit pupil is why 1:7
ratio binoculars are sometimes called "night glasses," because they provide
the largest exit pupil that the human eye can accommodate, and therefore the
brightest images.
This means that 1:7 ratio binoculars give the brightest views of nebulae and
star fields in a dark sky. (Binoculars with a ratio greater than 1:7 would
produce an exit pupil larger than the human eye can accommodate and some of
the collected light could not enter the eye.) But in a moonlit or
light-polluted sky, 1:7 binoculars also provide the brightest sky
background, drowning out faint stars and nebulosity. So for variable star
observers, a power-aperture ratio of 1:5 or smaller is preferable. We want
to darken the sky background and see fainter stars.
Nonetheless, all types of binoculars are useful for variable star observing.
Use whatever binoculars you have! My own working set includes 4x30, 7x35,
10x50, and 20x60, and I occasionally use a pair of 25x100 at a club
observatory. It should be noted that binoculars can magnify too little for
optimum astronomical use. I can't see stars much fainter than about
magnitude 6.0 with my 4x30s, because they don't magnify enough to fully
exploit the available aperture, but these small binoculars are excellent for
estimating variables in the 4th to 5th magnitude range. These variables are
a little too faint to estimate easily with the naked eye in a bright sky and
too bright for easy observation in more powerful binoculars. The 7x35s
reach magnitude 8.0, the 10x50s magnitude 9.0, and the 20x60s magnitude 10.0
in a fairly dark sky.
Some observing tips can improve the observation of variable stars with
binoculars. First and foremost, many modern binoculars are now produced
with orange or green objectives to penetrate haze – do not use binoculars
with colored lenses to estimate variable stars!
Also keep in mind that binoculars are altazimuth instruments (with hand-held
binoculars, you are the mount). This means that field rotation effects
cannot be avoided. To minimize errors caused by the changing angle between
the variable and each comparison star, bring each star to the center of the
field of view before deciding on your estimate.
Binoculars are intended for hand-held use, which is fine for stars well
above your binoculars' limiting magnitude (though one disadvantage of
hand-held binoculars is that you have to reacquire the field every time you
look away to check a chart). When observing dimmer stars, you can increase
your faint limit by at least 0.5 magnitude by resting an elbow on a fence
post or bracing the binoculars against the side of a utility pole or the
corner of a building.
Mounting binoculars on a photo tripod produces an even steadier view, but it
is difficult to use tripod-mounted binoculars when observing high in the
sky. The best observing investment I ever made was the purchase of one of
those "parallelogram" binocular mounts for my 20x60s. It allows me to
effortlessly raise and lower the binoculars, lets me get underneath to
observe near the zenith, and stays fixed on the field of view when I look
away to consult a chart.
Unless you observe from a desert location, dew is the greatest enemy of
binocular observers. Binoculars should be kept capped whenever they aren't
being used. Styrofoam cups make excellent insulating caps. I pop them over
the objectives whenever I am not actually looking through my mounted 20x60
binoculars. I keep smaller binoculars in a covered storage tub when I'm not
actually using them. Simple dew shields for each objective can be made from
rolled cardboard and adhesive tape. During the warm, humid summer months, I
have found that electric anti-dew heaters are essential during long
observing sessions (and dew heaters keep frost from forming in cold
weather). Alternatively, a hair dryer is noisy and has to be used again and
again, but it will do the job.
The AAVSO program includes hundreds of variables that can be observed
through all or part of their range with binoculars. Some of our top
observers have never used any other instrument.
Can variable star estimates made with binoculars contribute to "real
science"? Binocular observations are just as useful as estimates made with
large telescopes. A variable of a particular type has exactly the same
scientific potential whether it is 6th magnitude or 16th. If you observe
stars that are appropriate for your aperture, quality of the estimates is
the only consideration.
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3. THE STORY OF A VARIABLE STAR OBSERVATION - Glenn Chaple
THE MAGIC OF WEB OBS
On a cool evening in late October, I placed a reflecting telescope in an
open area of my back yard. Peering into the finder, I aimed the scope
towards the wide stellar pair zeta and theta Ursae Minoris in the Bowl of
the Little Dipper. A star-hop from zeta and theta brought me to my quarry –
the Mira-type variable S Ursae Minoris.
Alternating glances between the eyepiece and an S UMi "b" chart (illuminated
by a red flashlight), I selected a comparison star brighter (mag 7.8) than S
UMi and two that were fainter (mags 8.5 and 8.9). Several quick glances
between S UMi and the comparison stars, plus an out-of-focus study of the
field convinced me that S UMi was slightly brighter than the magnitude 8.5
comparison star. On a specially-made data sheet, I recorded the following
information: TIME/JD: 30 October 2005 at 9:44 pm EDT (= J.D.
2453674.6), STAR: S UMi, MAGNITUDE: 8.4, COMP STARS: 7.8, 8.5, 8.9.
Early the next morning, I accessed the AAVSO website on my home computer.
Clicking on "Web Obs," then logging in with my AAVSO observer code and a
password, I was ready to report my observations for S UMi and the 56 other
variable stars I viewed that evening. When finished, I carefully checked the
accuracy of my entries, made the appropriate corrections, and then pressed
"Logout & Submit Observations." A "Thank-you" message meant that my data had
been received by AAVSO Headquarters.
Every ten minutes, all newly received data are downloaded into the AAVSO's
main database. While I waited, I explored other parts of the AAVSO website.
I looked for updates under the "News and Announcements" section. A request
to "Help us create a map of AAVSOrs" piqued my curiosity. That heading
brought me to an outline map of the world, covered with little balloons –
each representing an AAVSO member. By clicking on a balloon, I got the name
and address of that member, plus a "shoutout" message, and, in many cases, a
photo. Filling in the info in the "Add Yourself" box, I added my own little
balloon to the map. If you haven't yet joined this "Map of AAVSOrs," do it
today!
Once ten minutes had passed, it was time to see the fruit of my labors. From
the menu on the AAVSO main page, I selected "Quick Look." In the appropriate
box, I typed in "S UMi," then clicked on the "SEARCH" prompt. Within
seconds, I was looking at a chronological listing - most recent, mine! - of
all S UMi observations forwarded within the previous few weeks. It was
gratifying to see that my magnitude estimate was comparable to those of
other AAVSO members who viewed S UMi around the time I did. But the best was
yet to come! I clicked on the "Lightcurve" prompt, located to the right of
my S UMi data. In less than a minute, a light curve of S UMi dramatically
showing the star's behavior for the previous 18 months appeared on the
screen. Each observation was denoted by a red dot, except for mine, which
appeared blue. Every observation of S UMi I had made since the spring of
2004 showed on the light curve (thankfully, they fit nicely with all the
others!). And there, at the recent end of the light curve was my observation
from the previous night. Like a solitary note from a musician, my one single
observation, combined with those from dozens of AAVSO members, had produced
this beautiful symphony of a light curve!
Think of it. Thanks to Web Obs, you can make a brightness estimate of a
variable star, go indoors to your computer and immediately forward the data
to the AAVSO. Then, within minutes you can see that observation plotted on a
light curve for that star. That, my Friend, is immediate feedback!
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4. STAR PARTYING 101 - Haldun Menali
Did you know that scientists estimate the planet Earth is home to
approximately 1.8 million species? The most dominant species is of course,
Homo Sapiens, meaning all of us! Today I will talk about a little less known
species, namely Homo Nocturnalis or night dwellers, analyze their kind of
ritualistic behavior called ‘star partying', and provide with some helpful
hints to any other people considering to attend one. Homo Nocturnalis may
not be a scientific classification, but they are there for real. In some
circles these species are called ‘amateur astronomers or stargazers' and
they are believed to be somehow mutated from Homo Sapiens by the call of
nature.
Let me begin by mentioning the main characteristics of a star party:
1) First, it is a gathering of night sky lovers in groups ranging between a
dozen to several hundreds, generally held annually.
2) Second, star parties can be at local, regional or national level, in the
order of increasing attendance.
3) Lastly, these gatherings usually take place many miles away from urban
centers where the sky is washed out with bright lights. Further you go away
from cities, darker gets the sky, and in a minute we'll see why this is
important in star partying.
I can almost hear you saying ‘why star partying in the first place'?
1) Mainly, star parties allow stargazers observe celestial objects under
quite dark skies. Most of the night-time objects are faint, and darker the
sky, the better the contrast and the details one can see. Some places are so
dark that Milky Way (our own galaxy) looks like a colorful chandelier
hanging in the sky! Recently, I read a story about a young stargazer and his
first star party. This novice fellow, after observing a while, started to
pack up his scope suddenly. When a veteran observer asked to why, he
answered that clouds started to move in from the east. The old hand chuckled
and told him that this is the Milky Way rising over the horizon!
2) Also, say, you are willing to buy a telescope, but not sure which one to
pick. As many stargazers bring their armada of telescopes to star parties,
these gatherings offer a chance to check out a great variety of telescopes
before you buy one. Members of Homo Nocturnalis are eager to let you ‘test
drive' their scopes which will give you hands-on experience in using one.
3) The saying goes: ‘happiness grows by sharing'. Enjoying the night sky
also grows when it is shared at star parties by fellow stargazers. During
these gatherings, you will have a chance to make new friends, find mentors
who will guide you into the hobby, or just plainly share the joyful moments.
Finally, you may ask ‘what do I need to bring to a star party'?
1) Well, most and foremost, a flashlight covered with a red filter. Homo
Nocturnalis are very easygoing and friendly creatures, except when disturbed
by intense white floodlights! Since they hunt, err… observe in the dark,
their dark-adapted eyes become very sensitive to any kind of light except a
red one.
2) In addition, simple star maps will be helpful to find your way in the
sky. Especially after leaving suburban skies where less stars are visible,
in a darker location where literally thousands of sparkling jewels twinkle
up there, you'll be lost without sky maps.
3) Next, bring a scope or binoculars if you can: any size is good for a
first-timer. If you don't have one, don't worry. Your eyes alone are what
you will need to engulf the vastness of space. Alternatively, feel free to
peek through fellow stargazers' scopes.
Considering what we have just heard, star parties are fun places to be. Some
of their benefits are similar to camping out: to mingle with Mother Nature,
flee away from our busy day-to-day lives, and enjoy the beautiful night sky.
Since it can be very dark around, don't forget to have a flashlight handy.
But beware to cover it with a red filter, not to scare Homo Nocturnalis, who
are out there in the jungle with several telescopes hunting for … faint
objects.
Remember: night sky belongs to everyone. And veteran stargazers always have
open arms to newcomers to share the wonders of the night sky.
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5. CV COMMENTS - Mike Simonsen
The old adage "you can't believe everything you read" was never truer than
for cataclysmic variables of the type UGZ. Named after the prototype Z
Camelopardalis, the most distinguishing property of UGZ type CVs are the
"standstills" they occasionally undergo in their cycles. This is described
in the definition from the General Catalog of Variable Stars (GCVS): "Z
Camelopardalis-type stars. These also show cyclic outbursts, differing from
UGSS variables by the fact that sometimes after an outburst they do not
return to the original brightness, but during several cycles retain a
magnitude between maximum and minimum. The values of cycles are from 10 to
40 days, while light amplitudes are from 2 to 5 mag in V." Do all UGZs
exhibit standstills? Are objects that don't exhibit standstills therefore,
not UGZs? It would seem fairly straightforward from the GCVS definition, but
things are seldom as simple as they seem in the world of variable stars.
Since this article is intended for visual observers, we will discuss only
objects that have outburst magnitudes of 13.5V or brighter. Our primary
sources for information on type, position, magnitude range, period, etc.,
are the GCVS http://www.sai.msu.su/groups/cluster/gcvs/gcvs/ and the Catalog
and Atlas of Cataclysmic Variables
http://icarus.stsci.edu/~downes/cvcat/index.html. As you will see, even
these two well-respected sources don't always agree on the facts, and in
some cases both are wrong!
RX And- (0058+40) With a normal range of 10.3-14.0V, this star is easy to
follow at all times during its cycle in modest sized telescopes. A quick
look at the AAVSO light curve for this star for the last 700 days will show
two obvious standstills after outbursts. ( http://www.aavso.org/data/lcg/ )
The cycles are fairly short and the amplitude of the curve is 3-4
magnitudes. This is a typical UGZ, showing all the normal characteristics
defined in the GCVS.
TW Tri- (0130+31) Outbursting to 13th magnitude a little less often than the
40 days defined in GCVS, the case for TW Tri's UGZ-ness is less clear. There
are no obvious standstills in the AAVSO light curves, possibly because the
magnitude at which it might rest before returning to quiescence (15th mag?)
is too faint for most visual observers to record. Another very similar star
is VW Vul (2053+25). Outbursting as bright as 13.1 at times and having a
minimum in the 16th magnitude range, short standstills occur in the mid-14's
and can be difficult to follow visually.
KT Per- (0130+50) Listed as UGZ+ZZ in the GCVS, this suffix to the
classification is explained in GCVS as "ZZ Ceti variables. These are
nonradially pulsating white dwarfs that change their brightnesses with
periods from 30 s to 25 min and amplitudes from 0.001 to 0.2 mag in V. They
usually show several close period values. Flares of 1 mag are sometimes
observed; however, these may be explained by the presence of close UV Ceti
companions." Another explanation for dwarf nova oscillations (DNOs) and
quasi-periodic oscillations (QPOs) observed in cataclysmic variable stars is
proposed by Brian Warner in 2004PASP..116..115W - Publ. Astron. Soc. Pac.,
116, 115-132 (2004) - February 2004, Rapid oscillations in cataclysmic
variables. http://simbad.u-strasbg.fr/cgi-bin/cdsbib?2004PASP..116..115W The
interpretation of these modulations is that they are "magnetically channeled
accretion from the inner accretion disk for DNOs" and "magnetically excited
traveling waves in the disk for QPOs".
TT Ari- (0201+14) GCVS lists this star as UGZ. Downes online CV catalog
lists the type as vy/dq: In other words, they are not sure if it is a VY Scl
type, which exhibit sudden fades, or a magnetic variable, specifically an
intermediate polar, whose accretion disk is interrupted by the presence of a
strong magnetic field. Most other references describe it as nova-like (NL).
As far back as 1979 this star is referred to as a NL object. An early IBVS,
from 1979, IBVS 1622, TT Ari; describes fast photoelectric photometry on
this NL. http://www.konkoly.hu/cgi-bin/IBVS?1622
More recently, IBVS 5664, December 2005, describes the recent fading of this
star. Again TT Ari is described as a NL variable, in spite of the VY
Scl-like fading. TT Ari: Out from the Positive Superhump State
http://www.konkoly.hu/cgi-bin/IBVS?5664
This fading episode is apparent in the ASAS light curve for this star.
http://www.astrouw.edu.pl/cgi-asas/asas_variable/020653+1517.7,asas3,%20%20%204.292588,0,1000,0
It is also visible in any recent light curve from AAVSO data. No obvious
outbursts are shown in the long-term light curve of TT Ari, certainly not
every 40 days or less, so why is this one listed as UGZ in GCVS?
TZ Per- (0206+57A) Plot a light curve for this star going back 500 days and
you'll see a standstill episode centered on magnitude 13.5, beginning around
JD 2453375. It appears to last at least 100 days, but the end of the
standstill is ambiguous due to the seasonal gap in the curve. This is pretty
typical for TZ Per, making it a great star for visual observers to monitor.
Varying between 12.0 and 15.6, it is visible more often than not.
AQ Eri- (0501-04) This variable is listed as a suspected UGZ in GCVS,
however IBVS 5107 describes AQ Eri as a UGSU based on superhump
observations. ‘Superoutburst Observation of AQ Eri: Evidence for an
Anomalous Superhump Excess?' http://www.konkoly.hu/cgi-bin/IBVS?5107. The
Downes catalog does not include AQ Eri in its listings of UGZs. Is this
merely outdated information in GCVS? Does the presence of superhumps
preclude classification as a UGZ? Maybe not; read on.
CN Ori- (0547-05) This is a very active star, with a range of 11.0-16.2,
outbursting about every other week. But the light curve looks very much like
a UGSS to me. Try as I may, I don't see evidence of standstills in the data.
Perhaps, as with TW Tri, the standstills occur below the threshold of most
visual observers. But I would expect to see gaps in the outburst frequency
if this were happening, and I just don't see it. What magnitude does it park
at when in standstill? Are the standstills short-lived, or do they exist at
all? This star also seems to be at or beyond the amplitude limit described
in GCVS. Is this a UGZ?
Two more variables fit this mold SV CMi (0725+06) and AB Dra (1953+77). They
are both active stars and interesting to follow visually, but they appear to
be more UGSS-like than UGZ. AB Dra in particular, is so active I can't
believe it has time to go into standstill between its frequent outbursts.
Z Cam- (0814+73) This is the prototype of this class, and a great star for
visual monitoring. It ranges from 10.0-14.5V and will sometimes get stuck on
the way down to minimum at or around 11.5. The last standstill was
relatively short, and not very stable. However, the one before that lasted
almost a year!
AT Cnc- (0822+25) AT Cnc is included as UGZ in Downes et al, but not GCVS.
This unusual variable has been spending more time in standstill than in
outburst or quiescence in recent times. It is therefore not surprising to
find a great number of papers on AT Cnc in standstill, including this recent
paper co-authored by AAVSO's Elizabeth Waagen. 2005PASP..117..931S - Publ.
Astron. Soc. Pac., 117, 931-937 (2005) - September 2005 A recurrence time
versus orbital period relation for the Z Camelopardalis stars.
http://simbad.u-strasbg.fr/cgi-bin/cdsbib?2005PASP..117..931S
It was surprising to find this paper describing superhumps in AT Cnc in
standstill. Apparently, superhumps do not preclude inclusion in the UGZ
classification! 2004A&A...419.1035K - Astron. Astrophys., 419, 1035-1044
(2004) - June(I) 2004 Detection of superhumps in the Z Camelopardalis-type
dwarf nova AT Cnc at standstill.
http://simbad.u-strasbg.fr/cgi-bin/cdsbib?2004A%26A...419.1035K
More papers on AT Cnc in standstill seem to make it clear that this variable
is a UGZ. Unusual Slow Fading of Standstill in AT Cnc
http://www.konkoly.hu/IBVS/5001.html#5099
1999PASJ...51..115N - Publ. Astron. Soc. Jap., 51, 115-125 (1999)
Spectroscopic and photometric observations of a Z Cam-type dwarf nova, AT
Cancri, in standstill.
http://simbad.u-strasbg.fr/cgi-bin/cdsbib?1999PASJ...51..115N
SY Cnc- (0855+18) Varying between 10.6 and 14.0, this active UGZ is always
visible in modest telescopes. Lying so near the ecliptic presents problems
as the moon passes through Cancer each month, and occasionally a bright
planet, like Jupiter, will plant itself right in the field, making
observations interesting and a bit difficult.
AH Her- (1640+25) This is another fairly typical UGZ. The range from
outburst to quiescence is 10.6-14.7, with occasional standstills around
12.5-13.0 after outbursts.
UZ Ser- (1805-14) UZ Ser is misclassified in both GCVS and Downes et al. As
early as 1987 standstill behavior was observed in UZ Ser.
1987JAVSO..16...91D - J. Am. Assoc. Variable star obs., 16, 91-93 (1987)
Unusual behavior of UZ Serpentis. http://simbad.u-strasbg.fr/cgi
bin/cdsbib?1987JAVSO..16...91D More recently, this star was included as one
of 16 examples of UGZ. 2005PASP..117..931S - Publ. Astron. Soc. Pac., 117,
931-937 (2005) - September 2005 A recurrence time versus orbital period
relation for the Z Camelopardalis stars.
http://simbad.u-strasbg.fr/cgi-bin/cdsbib?2005PASP..117..931S It seems to be
general knowledge amongst many that this star is a UGZ, but it is not
included as such in GCVS or Downes et al.
V1504 Cyg- (1925+42) GCVS lists this star as a suspected UGZ. Downes et al
lists it as UGSU. Considering the fact that both normal and super outbursts
have been observed and superhumps have been detected in outburst, this star
must be considered a UGSU. This is in fact the subject of IBVS 4532,
November 1997, Confirmation of the SU UMa nature of V1504 Cyg
http://www.konkoly.hu/cgi-bin/IBVS?4532
EM Cyg- (1934+30) This is a very active UGZ in a beautiful star field in
Cygnus. It ranges from 12.5-14.4, with short standstills in the low 12th mag
range. This is also the only known case of an eclipsing UGZ, so the accurate
type is UGZ+E.
FY Vul- (1937+21) Listed as UGZ in Downes and GCVS, this CV has an outburst
cycle between 30 and 50 days, but also shows some quasi-periodic variation
on shorter time scales, perhaps 15-20 days. The amplitude of variation is
rather small for a UGZ type dwarf nova. It has been suggested that this star
and V1101 Aql may actually represent a previously unrecognized group of
low-amplitude dwarf novae (IBVS 4766, 1999).
http://www.konkoly.hu/cgi-bin/IBVS?4766 Ranging from 13.4-15.3V this very
active star is doing something every night.
V1285 Cyg- (1941+35) Listed in GCVS as a suspected UGZ, this star is
actually a SR as described in the paper 1987A&A...185..203B - Astron.
Astrophys., 185, 203-205 (1987) The reclassification of the supposed dwarf
nova V1285 Cygni as a semiregular variable.
http://simbad.u-strasbg.fr/cgi-bin/cdsbib?1987A%26A...185..203B
EV Aqr- (2101+00) Listed as UGZ in both GCVS and Downes et al, here is
another case where both catalogs have it wrong. EV Aqr is obviously a SR
with a period of roughly 124 days, ranging from 11.2-14.0V. This can be seen
clearly in the ASAS data for this star.
http://www.astrouw.edu.pl/cgi-asas/asas_variable/210618+0052.7,asas3,%20124.919464,0,1000,0
HX PEG- (2335+12) Although not classified as UGZ in either GCVS or Downes'
catalog, HX Peg exhibits obvious standstills as well as the outbursts and
quiescent periods that generally describe UGZ-like behavior. It is variously
described as UGZ in other sources (Honeycutt et al. 1998 and the
aforementioned 2005PASP..117..931S - Publ. Astron. Soc. Pac., 117, 931-937
(2005), but not the two catalogs we have examined.
Another puzzling fact seems to contradict the accepted normal behavior of Z
Cam variables. It is generally accepted that standstills are triggered by
outbursts, and that standstills always end with a fade to quiescence. This
is stated plainly in Cataclysmic Variable Stars, How and Why They Vary by
Coel Hellier (pp. 73-74). However, both AT Cnc and HX Peg have been known to
go into outburst from a standstill. Does this fact make them non-UGZ, does
it make them a special sub-group of UGZ or does this throw a wrench into the
current models of enhanced mass-transfer sustained by enhanced irradiation?
How do these systems ramp back up to outburst levels after entering a
standstill? I don't know, but clearly the observational evidence does not
always agree with the theories.
So, where does this leave the visual observer interested in Z Cam type
variables? I'd say it puts you in great demand. Obviously, there is much to
learn about these CVs and there are plenty of examples bright enough to
follow and active enough to keep your interest for years to come.
Unfortunately, there is no one definitive list of UGZ type CVs from which to
pick your targets. Don't waste your precious observing time on EV Aqr and
V1285 Cyg if you want to observe CVs. Do keep an open mind and don't accept
everything you read as gospel.
Your observations may help shine a light on a previously suspected UGZ, or
help to classify a new type of variable, or just add to the important data
and general knowledge of CVs. It is your data that researchers use to create
models of CVs and try to untangle the mysteries of their behaviors. And it
is the unpredictable nature of CVs that keeps observers observing them night
after night, year after year. Who knows, maybe tonight AT Cnc will go into
outburst from a standstill. We'll never know if you don't get out there and
make the observations.
Good luck and clear skies to you all.
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Good observing!
Gamze Menali,AAVSO Technical Assistant (MGQ)
Aaron Price, AAVSO Technical Assistant (PAH)
Mike Simonsen, AAVSO Observer (SXN)
Copyright 2002, American Association of Variable Star Observers
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