Lightcurve: T Cep

Posted on June 3, 2014 by Gustav Holmberg

First in the series of posts on lightcurves is T Cep, which has become one of my favorite variables. It is circumpolar, which is always a nice thing – no season gaps in the light curve. Also, it clears the neighboring five storey house during winter and spring, which means that I can follow it all year around from my backyard, without moving about. 15×70 suffice most of the time, but I need a telescope to pick it up near minimum.

I’ve followed T Cep since late October 2011, through three maxima and two minima. The minima look more or less the same, while the maxima have quite different forms:

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Lightcurves

Posted on May 27, 2014 by Gustav Holmberg

I’ve been observing variables since late October 2011 (plus a stint as a variable observer as a student in the late 1980’s), so for some variables I have now collected so many observations that I can plot light curves spanning reasonably long periods of time. I thought I’d begin an irregular series of posts of such light curves here on the blog.

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Nova Delphini 2013

Posted on August 15, 2013 by Gustav Holmberg

Koichi Itagaki has discovered a bright nova in Delphinus. After spectroscopic confirmation, it got the official designation Nova Delphini 2013.

At first, the sky over Lund was cloudy. I waited and waited, but at about 02 local time (00 UT) I gave up and went to bed. However, some 45 minutes or so later I awoke and decided to leave bed and was greeted with a clear sky!

The nova was easy to find and I estimated its brightness to be 6.0 at August 15, 00.50 UT using 6×30 and 15×70 binoculars. The sequence used was an AAVSO chart, with convenient comparison stars at 5.7 and 6.2.

After that, the nova appears to have brightened somewhat:

Looking forward to following this bright nova!

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Bright supernova

Posted on July 21, 2013 by Gustav Holmberg

I observed SN 2013DY tonight: July 20.928 UT, 13.1.

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A new Algol variable

Posted on July 16, 2013 by Gustav Holmberg

H. Bengtsson, P. Hallsten, A. Hemlin, G. Holmberg, T. Karlsson, R. Wahlström, T. Wikander, “V2331 Cygni is an Algol Variable With Deep Eclipses”, has just been published in JAAVSO. Read it here.

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Variable star observers meet in Gothenburg

Posted on April 16, 2013 by Gustav Holmberg

I spent last weekend attending the 2013 spring meeting of SAAF/V, the variable star section of SAAF, the Swedish association of amateur astronomers.

First, variable star observer extraordinaire Hans Bengtsson received SAAF’s Amateur Astronomy Award for his longtime work in variable stars and other parts of amateur astronomy. While announced at the Värmland Star Party, Hans now received the award diploma from SAAF’s Jan Persson. He is truly a worthy receiver of the award, not only for his contributions to the field from the late 1960’s and onwards, but also for his continuing work with the variable star section. It is such a boon for the variable star group to have access to Hans’ deep knowledge of variable stars.

There were several presentations and discussions focusing on digital technologies. Robert Wahlström presented his more or less automated setup using, among other things, ACP scheduler, and we discussed and compared our experiences using remote telescope facilities such as iTelescope, Sierra Stars, Bradford Robotic Telescope and AAVSOnet.

Tomas Wikander was appointed new leader of SAAF/V. Furthermore, there were discussions of new discoveries and ongoing observing programmes. Tomas Wikander presented his recent discoveries of three new short-period variables, one of them a rare high amplitude delta Scuti star. We also discussed the current status of our programme to observe 50 obscure mira variables, and V2331 Cygni, discovered last autumn to be an eclipsing variable with deep minima. Plans for future programmes were drawn up, as was SVO, our magnificent database run by Thomas Karlsson.

Hosted by Slottsskogsobservatoriet, the public observatory at Gothenburg, the meeting was a great success. I am already looking forward to the next meeting.

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Värmland Star Party

Posted on March 14, 2013 by Gustav Holmberg

I spent last weekend in lovely Lysvik, where the annual Värmland Star Party takes place under a dark sky. Everything was great! Got to meet interesting people, hear interesting talks – not the least Johan Warell’s on comets and how to observe them – and the sky was clear for one and a half nights out of two. What’s more, there were several variable star observers there to talk shop with.

SAAF, the Swedish Association of Amateur Astronomers held its annual meeting on Saturday. SAAF also presented two awards: the Margareta Westlund award went to Thomas Karlsson for his work on variables (his observations of the eta Aurigae eclipse, his development of the SVO database, and his studies of O-C statistics of miras), and the Amateur Astronomy Award went to Hans Bengtsson for his longtime and ongoing enthusiastic efforts to spread knowledge about variable stars and other celestial phenomena.

Johan Warell, right, presents the Margareta Westlund award to Thomas Karlsson


During the observing sessions, when I was not recuperating from the -14 degrees Centigrade by visiting the nearby meeting rooms to drink coffee and eat hot dogs while chatting away with fellow amateurs who temporarily escaped the cold, I mostly observed together with Tomas Wikander. Tomas had brought his 12 inch SkyWatcher Flextube Dobsonian and he kindly let me join in, we had a great time with a mixed diet of variables and deep sky objects. The sky was very good, almost a magnitude better limiting magnitude than here in Lund. NGC 4565 was a wonderful sight, as was M51. I noted at least two personal firsts: the zodiacal light and the Horsehead nebula, the latter helped along with Johan Kärnfelt’s H-beta filter.

Tomas Wikander observes the sun through one of the many h-alpha telescopes set up at Värmland Star Party during the day


The Värmland Star Party, deep in the forests of Värmland by the lake Fryken, has been run for more than twenty years by a group of amateurs known in Sweden for their aperture fever, is highly recommended!

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Solar observing

Posted on March 4, 2013 by Gustav Holmberg

I used to observe sunspots with my 60 mm refractor during the 1980s and reported the observations to the solar section of SAAF, the Swedish amateur astronomical association.

Recently, my curiosity about what the sun is up to grew and I started counting sunspots again in January. February was awful, weatherwise, otherwise its great to be observing sunspots again. I report my observations to SIDC, the international sunspot data centre, as well as to SVO, SAAF’s variable star database, which also tracks solar activity.

Not much of activity for a maximum year, but still it is interesting to follow the sun’s activity from day to day.

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Nova Cephei 2013

Posted on February 11, 2013 by Gustav Holmberg

I’ve complained about the dearth of northern novae, but now there’s one shining not exactly bright but still easily observed in Cepheus.

I first heard about the object on the CBAT transients page some six hours after it had been discovered by the japanese nova hunters Koichi Nishiyama and Fujio Kabashima. That was during daytime here in Sweden. I posted a short message on Astronet.

There was no official sequence of comparison stars established yet, so instead I prepared a chart using visual magnitudes from the Tycho catalogue which I manually entered on the chart I had plotted using the AAVSO VSP. Finding the nova was easy: it is close to V Cas which I have observed earlier, so I knew the part of the sky, and I estimated the nova to be magnitude 11.5.

The sky was clear in other parts of Sweden as well, and several fellow Swedish amateurs observed the object on the evening on February 2. Hans Bengtsson observed it from his balcony observatory in central Gothenburg (Hans’ observation is the first, to date, recorded in the AAVSO database), Johan Kärnfelt picked it up with his 16 inch on the island of Brännö as did Robin Andersson with his new 14 inch telescope, while Timo Karhula observed with his 25×100 and Robert Wahlström measured it on CCD images (his three colour measurement in B, V and R, is to date the first multi-colour photometry reported to the AAVSO database). The next day, Tomas Wikander picked it up and Thomas Karlsson has observed it using a remote facility.

Then came the clouds, and neither I nor any other member of SAAF/V has seen the nova since February 3, but I hope to catch sight of Nova Cephei 2013 once more before it gets too faint. By now it has lost about a magnitude and is something like 12.6.

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New RCB and DY Per variables

Posted on January 17, 2013 by Gustav Holmberg

R CrB (AAVSO)

We live in exciting times, at least if one’s interests are RCB variables. Several of the better known RCB variables, including the DY Per subcategori, are in active states. SU Tau is presently below mag 17; Z UMi is emerging from a minimum began last summer that took it down to below 18, it is now at 13.5; R CrB is slowly moving up but is still in a very long minimum, began in 2007; DY Per began a minimum in October that took it down to 16.

The autumn-winter 2012-2013 minimum of DY Per.


But there are also other reasons why these are intriguing times for RCB watchers. Such stars are few and far between, and for a long time only a small number were known. However, new search strategies are yielding rewards and the number of known or suspected RCBs and DY Pers are increasing as several groups of astronomers are datamining large photometric surveys.

One recent paper is a paper by Miller et al1 which uses machine learning tools on ASAS south photometry to look for the telltale signs of RCBs and DY Pers. (One wonders, by the way, when ASAS north will be released, and what new RCB candidates might be found there?)

One of their findings is ASAS 053302+1808.0, a carbon star which is a candidate for a new RCB/DY Per star.

I thought might have a look at what it is up to this observing season.

  1. A. A. Miller et al, ”Discovery of Bright Galactic R Coronae Borealis and DY Persei Variables: Rare Gems Mined from ACVS”, The Astrophysical Journal 755 (Augusti 1, 2012): 98. Arxiv version [↩]
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