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recently spoke of cataclysmic variable stars when I referred to the eruption of UV Persei. There are a handful of these, which have the least brightest, who have come to be the most observed. One of these is SS Auriga coordinates (2000.0):

RA: Decline in June 1913
22.43 +47 44 25.4

in SS Aur minimum (top) and outburst (bottom)

SS Aur is a cataclysmic variable quite widely, between 10.8 and the 15.8 or 16, representing a difference in brightness of about 100 times the minimum to Max. Rashes occur approximately every 100 days.

Charter observation aur SS (AAVSO)

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More about GK Persei night

In the previous post I spoke of GK Persei cataclysmic variable, without realizing that it had entered one of its quasi-periodic outbursts.

curve generated from the database of the AAVSO

These systems usually alternate long and short eruptions. And for now it This time is quite long, in which GK Per and takes about 20 days above the scale 12. As often happens in these maximum-length, are usually not flat, but they will experience a slow increase in brightness after the quick burst.

at this stage is particularly interesting to study the brightness variations of small amplitude (sometimes not so small) that occur in time spans of hours. They are a real window to watch the behavior of the binary system that causes all the variability in brightness.

These short periods time variations usually appear somewhat recurring charged with high frequency, these are the eclipses between components of the binary system, a feature that occurs almost all cataclysmic variables since most have a favorable inclination to offer the eclipses. However, the appearance of the brightness curve is continually changing and is influenced by the accretion disk (around the compact component of the system), which is the element that brings more light to the brightness of the system. This album has its own rotation and revolution combined with the dual system will result in a whore complex variation, which combine either period.

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seems harsh winter has left us a few days. If we go into spring on Saturday, but still take some time to see their effects on weather, climate and the start of a station always keeps a gap with the astronomical beginning.

between front and squall But we can take a day or two at most, with clear skies in which to move the telescope back and return to observations. In my case, is again to take pictures to make the photometry. With so many cloudy nights lost a lot of practice and there are times when you do not have to be sure you remember how to operate the equipment.

The night looks very quiet, no wind, and a pleasant outdoor temperature of 14 degrees. This is especially convenient, since having the telescope inside the room air has to be balanced with the outside, and I have the assurance that these conditions will pretty quickly. I can thus assure an absence of severe turbulence that might degrade the image resolution.

After my experience in the past two winters I consider, if not change my place of observation, have the team standing in the raw cold nights. While I can still sacrificing to cool the house by having the window open, the poor results I get I have not been compensated for all the effort, since in these conditions of intense cold have taken hours to balance the air, a period in which, my batch of photos were terrible. But in the meantime, enjoy playing more favorable nights, despite being shorter.

I opened the night with GK Persei, the former Nova Persei 1901. Although it has been more than a century after its explosion, the cataclysmic variable star continues its current activity in the resting state, and undergoes outbursts every 500-600 days, about two magnitudes of amplitude, as we see, similar to novae dwarf, well below what was his classical nova explosion in 1901. By the way, now is in a state of eruption on the scale 12, a magnitude above normal brightness.

But, alas, have caught the star very low, and is hiding behind the building opposite, I have not had time to take more than one take, with the building across the "swallowing" the star field. But there is still night, and there are other objects waiting to be recorded by the CCD.

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A Variable Star: An Introduction (III) When observed, how often, where will I send my comments?

Programming comments

The field of variable stars has an additional attractive feature that may appeal to the amateur. This is none other than the possibility of organizing the observations by optical equipment, the usually accessible area of \u200b\u200bsky, the time available to observe the dark sky conditions and as many conditions as possible.

Despite the above before, the new observer must bear in mind that it is essential to acquire practice in the visual photometry and take time to get to know the behavior of the variables that will be monitored. It is therefore absolutely necessary to start with enough bright variables with an amplitude of brightness fluctuation is large, about 4 or 5 magnitudes or more.

Pulsating variable stars of long period or type MIRA are those fulfilling the conditions, with amplitudes of 2.5 magnitudes below and periods between 80 and 1000 days. These are perfectly noticeable brightness variation from week to week following a fairly regular pattern that will awaken the interest of the neophyte. In keeping with its long period of variation, ee.vv. MIRA type must be observed with a periodicity of 7 days, as recommended in the latest round of the AAVSO, trying to avoid more frequent measurements, which alone would result in the accumulation errors. In this phase, the observer also may continue semiregular pulsating stars.

These fluctuations have maximum brightness of 2.5 magnitudes and periods between one month and 1000 days. The ee.vv. semiregular have some resemblance to the long period, but even having a similarly slow their evolution pattern of variation is not free of irregularities, so the

brightness curve T Cephei. Mira type.

variability should not be surprised if you encounter one of these stars remains several weeks in the same magnitude or expected value is less than the maximum, these irregularities, far from discouraging the viewer, are a great incentive to the extent that involve a component that is often unpredictable circumvent established patterns on these variables. Its maximum frequency is seven days observation is perfectly valid but monitoring every 10 to 15 days, especially the star appears to be in a rather static phase. Copies of semiregular variables with high apparent brightness are very numerous in the entire sky, and this, coupled with its moderate size makes it ideal for star watchers are equipped with binoculars.

brightness curve W Cygni. Tiling.

pulsating stars of long period and semiregular correspond to late spectral types and have a pretty intense orange color. That is why we must estimate their brightness quickly because otherwise we tend to overestimate its luminosity, as a consequence of Purkinje effect (whereby the night vision eye has over sensitivity to red light).

When we acquired more experience we can begin to look at other types of variables. The ee.vv. Eruptive or cataclysmic be the next step. This kind of star, it behaves impossible to predict, reason must be observed every clear night, especially the subtypes U Geminorum, Z Camelopardalis, Nova and Supernova, whose brightness variations become extremely fast. Other kinds of eruptive: Eruptive Irregular Symbiotic Stars, R Coronae Borealis Stars Quasi-Novas (P Cygni), etc, can have periods of slow change in brightness, so observations must be reduced to once every 7 days unless detected or has notice of a particular activity. On the other hand, Novas and Supernovas deserve a separate space for his great showmanship, we merely point out that any fan variability

brightness curve SS Cygni. U Gem type.

minimally experienced should not miss the opportunity to see the 2 or 3 novas that usually appear in the sky each year or one of the few extragalactic supernovae that become visible in mid-aperture telescopes, these are rare events where you have to dump a special observational effort to achieve progress in their knowledge. Of special interest are objects of type U Geminorum or dwarf novae. They are stars who stay for long periods in a rather weak brightness (minimum brighter UGem of all is the SS Cyg, with 12.1m) to that in a moment that usually comes with some but not strict periodicity, increases its brightness by 4 magnitudes or more (an increase of 40 times luminosity) within one or two days, the star will remain at maximum brightness several days, even a week, after which it returns to its original condition within days. The Z Camelopardalis-type variables have, in turn, an activity rise and fall of about 4 magnitudes continuously repeated over a period of two weeks until they suddenly fall into a magnitude 2 / 3 between the minimum and maximum experience almost no variation. This rest period You can reach extending to more than one year, with no way of knowing exactly when it ends. Dwarf novae, for his showmanship and his unpredictable behavior constitute a formidable challenge to the observer, who will try to watch each night after night waiting detect eruptions. Unfortunately this type of eruptive variables are

brightness curve SS Aurigae. U Gem type.

maximum
tenuous (the brightest is that of SS Cyg, the 8.3m) minimum and weaker still. This forces us to realize that only we can get full with these stars if we have accumulated enough experience with other types of variables and if we have a telescope of aperture 20 cm minimum. As José Ripero, the variability more active in Spain and one of the first in Europe, writes in an article: "[...] (must) always start the race 'variability' by the most simple variables, since experience in this field is essential. There will be time to observe faint variables difficult "(Riper, 1986).

more advanced fans can go to look at other types of variables: eclipsing, Cepheid, RR Lyrae or others. Eclipsing binaries are charged and periodic variations of magnitude lasting about one hour, while Cepheids have periods of several days and amplitudes less than 1 magnitude. Types of variables are often difficult to see properly and that many others require study by means of photoelectric photometers. In any case, your observation is organized into a program and a specific methodology that we will not detail here.

An estimation of brightness as we perform with the visual method reports an interesting fact that no record would be meaningless. Targeted, for each observed variable star in one night:

1. the time of observation TU
2. description and name of the variable
3. including decimal Julian day, estimated magnitude
4. comparison equation (including the magnitudes of comparison stars and the observed differences with respect to the variable: m to ( to ) v (b ) m b) increases
6. used any notation that may be useful

all this in a notebook that will see all our observations.

During the session we will help of a flashlight with a filter that gives us a red light to make entries and read maps without glare and without having to interrupt our task to go to turn on lights.



How to publicize our work?

As soon as we started to accumulate estimates of brilliance week after week we will surely ask you the reason to follow a variable star for months and then years beyond mere curiosity. The fan may not know that there is a real demand for variable star observations from the professional astronomer.

An astrophysicist can investigate a star with great precision and detail through very large aperture telescopes and advanced technology, also providing space instruments that provide access to other regions of the spectrum. However, the thoroughness of his observations and the limited time available for these prevent the researcher continuously monitor both the objects of interest and simultaneously scrutinizing more than one of them.

Meanwhile, the fans, whatever your instrument of observation, is able to track the night sky and control every behavior of tens of variable stars. Therefore, the professional needs of the observations photometric engaged the fans, and for this purpose associations observers of variable stars are the intermediaries between the two groups. On the one hand provide the methodology, compared with sequences of maps and all sorts of information for the amateur observations made optimally. At the same time, make available to their files astrophysicists brightness measurements.

is strongly recommended that English fans starting in this field will be guided by active observer groups, grouped into lists e-mail as flashes :

http://es.groups.yahoo.com/group/destellos/

But without a doubt, this society is the most relevant AAVSO and mentioned above. Since its founding in 1911 (eleven years before the International Astronomical Union), meets in a database of over 8 million comments have been providing hundreds of Americans and observers around the world. Each year also serves a growing number of requests from professional astronomers and educators.

Edits for its members a magazine and a newsletter, apart from maintaining emergency alert service through which amateur observers praise provide data updates on some stars that are being studied by astrophysicists.

Located in our neighboring country, AFOEV variability brings together fans from France and other many countries, the purpose and success similar to the AAVSO. Observation also publishes maps and informational publications for its members. It is recommended that all observers working with variables from the beginning send comments on these two associations. If after the time the fan has a particular interest towards this field should consider joining the AAVSO or AFOEV . In any event, they will welcome all comments sent to them and gladly provide any information requested. Their addresses are:

AAVSO 49, Bay State Road
Cambridge, MA 02138 USA

aavso@aavso.org

http://www.aavso.org

AFOEV
Observatoire de Strasbourg 11, rue de l'Université

67000 STRASBOURG France

http://cdsarc.u-strasbg.fr/ afoev /

These associations and their observers are now such a contribution to astronomical research that have become the star tracking variable stars in the optical field in an almost exclusive amateur and making it a rung staircase leading to a better understanding of the universe, a place for everyone who willing to observe discipline and continuity.

References (originally published, a little dated, see this post for an updated bibliography)

(1). Levy, D., 1986. Observing Variable Stars. Sky Publishing Corporation.

(2). MacRobert, Alan, 1996. The Lure of Variable Star Observing. Sky & Telescope Vol 91 no. 3.

(3). Mayall, Margaret Walton, 1970. Manual for Observing Variable Stars. AAVSO.

(4). Ripero Osorio, J., 1986. Instructions to observe variable stars (I, II and III). Tribune

Astronomy, nums. 3, 4 and 6. Madrid.

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Variable Stars: An Introduction (II) visual estimate

observation methodology
Variable stars are an area of \u200b\u200bparticular interest to the amateur astronomer for two reasons:

1 - is the right person to continue their behavior on a regular basis to be impossible from a professional observatory regular observation of all variables listed.

2-the area of \u200b\u200bee.vv. is open all availability of instruments, since there are variables that can go bright to the naked eye, there are many that can be observed with simple binoculars, and the catalog is extensive and varied enough to be useful telescopes of all kinds.

To this we must add that the observation of e. variables is very demanding on the quality of the optics used and which are not indispensable exceptional conditions of transparency and darkness if we are not studying too faint stars, this means that since the city can keep a lot of variables with very simple telescopes . The task of the amateur in this field will consist of making a measure of brightness or variable star photometry in the study and repeated some time later.

With photometric measurements of different times we can reconstruct the behavior of the selected object. The relationship between date and brightness can be summarized and displayed in a Cartesian diagram, with time on the horizontal axis and the visual magnitude in the vertical axis graph called brightness curve.

photometric To begin our journey will be equipped with specific maps variable stars, which mostly edit AAVSO (American Association of Variable Star Observers) and AFOEV (French Association Observer Variable Star).

maps of type 'a' (on a scale of 5 'per mm) will allow us to locate the variable (probably also with the help of a detailed atlas like Sky Atlas 2000.0 or Uranometria), while the letters 'b' (60 "per mm) will allow us to identify the variable that we seek no error and measure its brightness when it is maximized.

The letters 'c', 'd' and 'e' (on a scale of 40 ", 20" and 10 "per mm, respectively) are available for faint variable stars or weak and will give us maximum field of view restricted and weaker comparison stars, we will use during phases of reduced brightness. Photometry we're going to make it visual, that is, from now on we only need your eye to measure the brightness of the variable.

Once we have located around this we will need to find two stars that we call stars of comparison, a brighter and a weaker one, and we will estimate the difference in brightness of the str. Comp. with e. treating variable assign one of the following degrees of Argelander :

• The grade 1 is set when you enter the variable and the comparison star is a nearly imperceptible difference in brightness, which is only appreciated after careful consideration.
• The grade 2 when the variable is set and e. comparison seem the same brightness at first glance, but soon we see a slight difference in brightness between the two.
• The grade 3 when set between the variable and e. comparison is a moderate brightness difference can be seen from the outset.
• The grade 4 is set when the difference in brightness between the variable and comparison star is remarkable.
• The grade 5 is set when the difference in brightness between the variable and comparison star disproportionate.

Thus we compare the first variable star with a star that has a lower brightness and then with another that is more light.

The brightness value of e. I obtrendremos variable by a simple formula given below:

var m = m to + (m b - m to ) * to / ( to + b )

where var m is the magnitude of the variable star, m to the magnitude of comparison star superior brightness and to the degree of difference between observed brightness; m b is the brightness of the comparison star brightness and lower b the degree of difference observed between this and the variable.

There are cases in which we can discern differences in brightness a little more ambiguous, in which we taking degrees in tenths, so, for example, if a difference of brightness was between 1 and 2 would take a degree 1.5.

This method, although it appears to us fairly intuitive, it is quite reliable. To analyze the degree of precision with which we could discern a difference nominally up to a tenth of a magnitude, which in practice boils down to a confidence interval between 0.2 and 0.4 magnitudes, which is a perfectly acceptable uncertainty in monitoring of stars with an amplitude of variation of 1.5 magnitudes at least, which are the are the program of visual observation.

The time reference we will use is the Julian Day (defined as the average number of solar days elapsed since noon on January 1 4713 BC), which provides a continuous time scale entirely without the changes it is always subject to the civil calendar .

The comments are always referred to the date and time is expressed in Julian day made with an accuracy of several decimal places. Observers have to do Julian Day calendar and tables for fractions of days from the time in universal time, in case you do not have software tools on your computer or on the web to calculate it. ;

not forget, at the time of calculation, the astronomical Julian days are days, that is, beginning at noon, universal time.

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Stars Variables: An Introduction (I) (Note that it fried)

had promised to publish a simple introduction to the topic of variable stars. As I already had written for many years, but was available on a page that no longer exists, I'll get it back through the blog VariaStar. I take it for good this remake if it is useful to pers onas that p irst time approaching the world of variable stars.

Variable Star: An Introduction (I)

A variable star is any star in the sky whose brightness is not constant but change with time. Although it is suspected that the Arabs already know the variability of Algol, Beta Persei, the first reference is to secure a star in the constellation of the Whale, which Fabricius observed in 1596 in the third magnitude when it was omitted from the maps, which called Mira (wonderful), and Bayer independently cataloged under the name omicron Ceti in 1603.

What appeared to be a few anomalies in the unchanging sky for astronomers of the seventeenth century were already more than three hundred by the end of last century and today are about 40000, which is why variable stars are a branch Astronomy independent today. However, and paradoxically, the importance of ee. vv. reside outside their own area, extending the full knowledge of the universe. Stellar variability responds to particular moments in the life of a star, or the interactions between the stars that make up double or multiple systems, or effects between a star and a surrounding material, or phenomena on the surface, etc, etc. Thus, in this way, variable stars are real testbeds to study the structure and evolution of stars, the fluids in the interstellar medium, exotic objects in the galaxy, or as many problems of astrophysics.

Classification of Variable Star

The variability in the brightness of a star can be caused either by:

1-fault of the star itself. In this case we Extrinsic Variables that are not ee. vv. strictly speaking, but rather specific instances of binary stars in which a hidden component of other observers. So this is also called eclipsing variables. Can be of three types: Type beta PerseiTipo beta Lyrae type W Ursae Majoris

2 - The physical structure and all kinds of processes that occur in the star. These are the stars Variables Intrinsic or Physics. This is the kind of ee.vv. to which we will pay more attention. There are two main types of ee.vv. Physical:

Pulsed . Have a brightness variation usually soft and maintains a clear schedule. May be of the following subtypes:

Cepheid (classical) (short-period Cepheids)


RV Tauri type


beta Canis Majoris type


RR Lyrae Type


Delta Scuti type


Look
Type

semiregular


alpha-2 type Venaticorum canum




Eruptive . Are sharp variations in brightness, not follow, in many cases, an appreciable frequency. They present 2 subtypes:


Eruptive Irregular


Eruptive Cataclysmic
Supernovae:
Type I
Type II

News:
Ballroom

; Glasses
; Very Slow

U Geminorum type

Z Camelopardalis Type

Type Z Andromedae (symbiotic stars)

R Coronae Borealis type

Nomenclature of Variable Star

Like ordinary stars, the variables are named according to the constellation to which it belongs, identified by a Latin letter beginning with R (with so as not to be confused with Bode star catalog, which uses the alphabet from A to Q) followed by the genitive of the Latin name for the constellation within which it is.
When it comes to Z name starts with two letters, beginning a series that runs from the RR to RZ. If more variables are found in pairs series will begin with S, T, etc, to Z, combined with the R, S, T, etc to Z. Also it is possible to do sets of 2 letters from A to Q combined with the letters A through Z.

With this system 334 can be classified variable stars in a constellation when recognizing new such objects shall be named with the prefix V and the serial number (which must be from 335), accompanied by the Latin genitive of the constellation name. There are also variables that receive the traditional name or the name of Bayer to be known long before the discovery of its variability: Beta Persei (Algol), Chi Cygni, for instance.

A variable star also receives a numerical designation, the number of Harvard, which corresponds to their coordinates in the epoch 1900.0. On the other hand, different kinds of variable stars are designated by the name of a star which is usually the first such discovery and is the prototype of behavior that is classified.

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A nova out of the ordinary

On March 10 some Japanese observers detected an explosion in the variable star V407 Cygni. The strange thing was the intensity of the blast, which reached a maximum brightness of 7.4, when often remain in the 13 sleep.

V407 Cygni is a symbiotic variable. Symbiotic star is called a binary star in which coexist with a very sharp contrast in their spectral types (ie, their surface temperatures). This difference is evident in their spectra, which were impossible to read until it was determined that responded to the combination of those for each component of a dual system. Similarly, in a symbiotic variable shows a very long period of revolution, which means that the hotter component (and small and compact) revolves around a star enough massive so you have to do it at a distance take years to complete one revolution. It should be a big star and cold, a condition that meets a red giant.

symbiotic variables are strange in their behavior, show regular variations similar to those of a Mira variable (which are variations of the red giant component, acting as such type of variable), can present occasional eclipses when the plane of rotation of the system is a suitable inclination, or, without a clear periodicity, flare or outburst "very similar to lso given in the so-called cataclysmic variables, by mechanisms quite similar.

The symbiotic are kind of all-in-one variable stars: pulsating, tiling, eclipsing and eruptive, and herein lies part of its interest in astronomical objects.

And it does not end here, the symbiotic also can erupt in a violent way, with much wider than a regular pop. It is an explosion similar to those of a classical nova, and is considered as a category of nova, we will refer to this as a symbiotic nova.

And this is what has happened to V407 Cygni. Around its compact hot component has been an accumulation of hydrogen gas to achieve higher levels of density and pressure conditions found to begin nuclear fusion that leads to Helio. This fusion takes place in an abrupt and explosive, which is manifested in the explosion of nova.

In the case of not knowing the progenitor of the nova can be identified as symbiotic by the length of the burst and its own spectral characteristics. But in this case we know the system has occurred, which is a symbiotic variable more or less well known.

From now until later this year is expected to V407 Cyg remains on a scale accessible to visual observation with telescopes modest. Can be an object of interest in the summer observations to be located in this constellation as typical summer as Swan.