Wednesday, February 12, 2020
Will Betelguese Brighten in the Coming Fortnight?
As has been reported widely, the red-giant Betelgeuse has been dimming and is now dimmer than has been measured visually in the last 50 years.
This has caused considerable excitement in the astronomical community, but although Betelgeuse is "close" to the end of its lifespan, it is unlikely to go supernova any-time soon (maybe 100,000 years from now).
There has been a lot of speculation over why Betelgeuse is dimming. The leading theory is that it is a chance alignment of it's natural variability cycle. Betelgeuse is a variable star with a complex cycle of dimming and brightening, there is a dominant period of 420 days, superimposed on a long period of 5-6 years and a shorter-term variability of around 180 days. An early Astronomers telegram at the beginning of the "fainting"suggests that the "the current faintness of Betelgeuse appears to arise from the coincidence of the star being near the minimum light of the ~5.9-yr light-cycle as well as near, the deeper than usual, minimum of the ~425-d period".
A more recent Astronomers telegram has reported improved modelling of these cycles and predicts if the cycles are the cause, Betelgeuse should start brightening on February 21 (± 7 days). That means it could start brightening as early at Feb 14 or as late as the 29th. Some more explanation and graphs are available at this Space Weather article (scroll down).
Whatever happens in the next fortnight and beyond, observation by multiple observers are required during this critical time period. See spotters maps and brightness guide stars below.
Regardless of cause, Betelgeuse is the dimmest and coolest it has been since photometry began 25 years ago, and may even have shrunk to 92% of its previous diameter.
Orion is readily visible. Betelgeuse is the bright red star below the "saucepan" of Orion. Red Aldebaran is almost the same height above the horizon as red Betelgeuse, making brightness comparisons easy.
In order to avoid the Purkinje effect, where red stars seem to become brighter the longer you stare at them, you need to keep shifting your gaze around. Try bracketing the star with observations of stars brighter and dimmer. to get a good comparison. A more comprehensive guide to observing variable stars is here. Different observers will have slightly different estimates. My last estimate was Betelguese was a trace under 1.7 and Les Dalrymple had it a trace over. Try not to let your expectations bias what you are seeing. Comparison sttar magnitudes are given below.
Labels: Betelgeuse, unaided eye observation, variable star
Tuesday, December 31, 2019
Betelgeuse continues its historic fade
Betelgeuse is a red giant star which forms a distinctive part of the Constellation of Orion the Hunter. It has shot to prominence recently as it has dimmed to levels not seen for over 25 years. It is now obviously dimmer than magnitude 0.85 Aldebaran and roughly as bright as Bellatrix, the next brightest star just to the north of Betelgeuse (see chart below). While there is a lot of excitement as Betelgeuse is likely to go supernova "soon", soon is probably 100,000 years away, and the current dimming has other explanations (see below).
While familiar to almost all casual observers of the night sky as the bright red star that forms the shoulder of Orion the hunter, most people were unaware until recently that Betelgeuse is a variable star with a complex cycle of dimming and brightening. While the variations in brightness are small they may form the basis of stories by indigenous Australians who were keen observers of nature.
As I said, the variability of Betelgeuse is complex, with a dominant period of 420 days, superimposed on a long period of 5-6 years and a shorter-term variability of around 180 days. The latest Astronomers telegram suggests that the "he current faintness of Betelgeuse appears to arise from the coincidence of the star being near the minimum light of the ~5.9-yr light-cycle as well as near, the deeper than usual, minimum of the ~425-d period".
It is possible that Betelgeuse is close to its minimum, so further observations are needed over the coming days. Towards the end of the week, the waxing moon will make it more difficult to estimate Belegeuses brightness.
In order to avoid the Purkinje effect, where red stars seem to become brighter the longer you stare at them, you need to keep shifting your gaze around. Try bracketing the star with observations of stars brighter and dimmer. to get a good comparison. A more comprehensive guide to observing variable stars is here. Different observers will have slightly different estimates. My last estimate was Betelguese was a trace under 1.6 and Les Dalrymple had it a trace over. Try not to let your expectations bias what you are seeing.
Labels: Betelgeuse, unaided eye observation, variable star
Friday, December 20, 2019
Betelgeuse Fades More
Betelgeuse is the bright red star below the "saucepan" of Orion. Red Aldebaran is almost the same height above the horizon as red Betelgeuse, making comparison easy. Aldebaran is magnitude 0.85 and is now visibly brighter than Betelgeuse.
Betelgeuse is a red giant star which forms a distinctive part of the Constellation of Orion the Hunter.
While familiar to almost all casual observers of the night sky, not may people know Betelgeuse is a variable star, with small fluctuations in brightness not visible to the casual observer. It typically ranges between 0.3 to 1.0 (in the stellar magnitude system smaller numbers are brighter than larger numbers). For a fuller explanation of Belegueses complex variability see my previous post.
A 2 year light curve of Betelgeuse from the light curve generator at the AAVSO. It's a bit messy because of all the observations , but if you pick out the yellow line you can see that it has now dipped to around magnitude 1.5 in the latest observations.It your sky is not covered by smoke of cloud at the moment go out now (well, its best to go out around 11:00 pm when the reference stars are high enough. for good comparisons. The Moon is not in the evening sky to interfere with the stars brightness. Nearby Aldebaran (magnitude 0.85) also red, is a good comparison star. Belatrix, the other shoulder star of Orion opposite Betelgueuses is magnitude 1.6. The middle star of Orions belt, Alnilam is magnitude 1.7 and Adhara in Canis Major is Magnitude 1.5. Achernar (magnitude 0.45), Alpha Crucis (magnitude 0.61) Mimosa (beta crucis magnitude ) and Beta Centauri (magnitude 0.55) are also good comparison stars but further away and harder to compare (see chart below).
Star Map via Virtual sky. Use your mouse to scroll around and press 8 when your pointer is in the map to set to current time.
Cloud cover predictions can be found at SkippySky.
Here is the near-real time satellite view of the clouds (day and night) http://satview.bom.gov.au/
Labels: Betelgeuse, unaided eye, variable star
Wednesday, December 11, 2019
Betelgeuse Fades
Betelgeuse is a red giant star which forms a distinctive part of the Constellation of Orion the Hunter.
While familiar to almost all casual observers of the night sky, not may people know it is a variable star, with small fluctuations in brightness not visible to the casual observer.
A 9 year light curve of Betelgeuse from the light curve generator at the AAVSO. It's a bit messy because of all the observations , but if you pick out the yellow line you can see the recent dip in brightness that has everyone excited.The variability of Betelgeuse is complex, with a
dominant period of 420 days, superimposed on a long period of 5-6 years and a shorter term variability of around 180 days. The 420 day variability was likely observed by Indigenous Australians and incorporated into their sky stories.
However now it has been reported that Betelgeuse has dimmed substantially, (see curve above) to a 25 year low (even though it is still bright to us). It is well worth keeping an eye on it, to see if it dims further.
What the dimming means is not clear. It is thought that Betelgeuse's variability is due to the star expanding and contracting in size, with dimming due to contraction. The unusual dip in brightness may be due to its' multiple cycles lining up, or possibly dust being brought up to the surface.
Betelgeuse may be getting a bit more attention as we expect it to go Supernova, but we don't expect that to happen for tousands, if not millions, of years from now.
At the moment getting a good fix on Betelgeuse's brightness will be a bit difficult, as the nealy full moon will make determining its brightness harder, but by the week end there should be enough time before the moon rise to get a good feel for it. Achernar (magnitude 0.45), Alpha Crucis (magnitude 0.61) and Beta Centauri (magnitude 0.55) and the red giant star Aldebaran (magnitude 0.85) are good comparison stars. All in all Betelgeuse will be an interesting object over the coming month.
Labels: unaided eye, variable star
Thursday, February 16, 2017
Mira nears Maximum
 |  |
| Westen horizon at 22:00 ACDST showing Mira and the other bright stars of Cetus. Stack of 9x15 second exposers 400 ASA, Canon IXUS. Stacked in Deep Sky Stacker. | Stellaium view of the western horizon at astronomical twilight, the location of Mira is indicated by the circle. |
Mira (omicron ceti), a star in the constellation of Cetus the whale, is a long period pulsating red giant and changes brightness from below naked eye visibility to a peak of round magnitude 2 (roughly as bright as beta Crucis in the Southern Cross) in around 330 days. Mira is predicted to peak with maximum of 3.4 around 23 February.
This image is the first time I've been able to capture Mira this cycle. Mira, bespite being low to the horizon, is already quite bright, around at least magnitude 3.7 (close to the brightness of Baten Kaitos, zeta (ζ) Ceti. Unfortunately, as it approaches peak brightness on the 23rd, it comes closer to the horizon.
Labels: variable star
Saturday, April 16, 2011
AAVSO Alert Notice 437: Campaign to monitor T Pyx throughout 2011 eruption
April 15, 2011
Further to AAVSO Alert Notice 436
(http://www.aavso.org/aavso-alert-notice-436), a fast photometry
observing campaign has been initiated by Dr. Bradley Schaefer
(Louisiana State University) to monitor the recurrent nova T Pyxidis
throughout its current eruption. (see also GRAS NEWS-Caught in the Act! Nova T_Pyxidis in Outburst)
Brief summary of eruption: The recurrent nova T Pyx was discovered in
outburst by M. Linnolt (Hawaii, United States) at visual magnitude
13.0 on 2011 April 14.2931 (JD 2455665.7931), and confirmed by
A. Plummer (Linden, NSW, Australia) at visual magnitude 12.2 on April
14.3847 (JD 2455665.8847) and S. Kerr (Glenlee, QLD, Australia) at
visual magnitude 11.3 on April 14.4410 (JD 2455665.9410). This is
the first outburst of T Pyx since December 7, 1966, nearly 45 years
ago. As of April 15.6271 (JD 2455667.12708), it had brightened to
visual magnitude 8.3 (A. Pearce, Nedlands, WA, Australia). If it
behaves as in past eruptions, it can be expected to brighten to
magnitude 6. All observations -- visual, CCD, and PEP observations,
and CCD time series -- are encouraged.
Campaign: Full details of the campaign may be found on the T Pyx
campaign information page (http://www.aavso.org/campaign-monitor-
recurrent-nova-t-pyx-throughout-2011-eruption). The following is
a description of the campaign summarized from that page:
"The goal is be to get nearly-fulltime coverage of T Pyx with time
resolution of minutes throughout the entire eruption up until T Pyx
is lost behind the Sun around the start of August. This will require
many observers, widely spaced around the world, each taking long runs
of CCD images. The eruption takes roughly 9 months to go back to
quiescence, but we will only go from now until the end of July (3.5
months) when T Pyx is lost behind the Sun.
"...V filter is preferred for CCD observations, with second choice
being B filter, third choice R, and last choice unfiltered. (T Pyx
should be magnitude 6-10 over this whole time interval, so a filter
will help against saturation.) To make for a uniform magnitude scale
by everyone, please use the following comparison stars:
COMPARISON: AAVSO="93" HD77862 09:04:09.4 -32:11:16 B=9.85,V=9.31
COMP2: AAVSO="69" HD77645 09:02:51.8 -32:26:24 B=6.90,V=6.93
COMP3: AAVSO="115" CD-31o6884 09:04:43.8 -32:24:47 B=12.12,V=11.52
Variable star (do not use):
AAVSO="84" HD77938 09:04:29.5 -32:26:54 B=9.49, V=8.44
Please use the COMPARISON star (AAVSO="93") for all the differential
photometry as it will have nearly the same colors as T Pyx. Use the
other backup comparison stars only if you have troubles with field size,
saturation, or SNR problems. With the bright stars and differential
photometry, T Pyx can be followed down low on the horizon.
"T Pyx is only one of ten known recurrent novae in our own Milky Way
galaxy. It has erupted in 1890, 1902, 1920, 1944, and 1967...we...are
not missing any eruptions in this time interval...Judging from the 1967
eruption light curve, the current eruption light curve will stall out
of its rise at around V=8 around 15 April, slowly rise to a peak near
V=6.4 around 20 May, slowly fade to V=10 by middle August, then have a
sudden drop by two magnitudes over the next 20 days (with drop being
invisible due to the Sun)...
"Recurrent novae...are one of the best candidate systems for being the
progenitor of Type Ia supernova. This progenitor problem is a long
standing sore mystery...Indeed, in last year's Decadal Survey, the
National Academy of Sciences identified the progenitor problem one of
the four most important problems in all astronomy...T Pyx...[is] the
lynchpin of many arguments and discussions for the progenitor problem.
The work on this eruption will largely be aimed at testing whether
T Pyx will become a Type Ia supernova.
"...Only one nova has large amounts of fast photometry...the recurrent
nova U Sco, which erupted in 2010. For this, I organized a large
worldwide collaboration of (mostly amateur) observers, and we measured
37,000 magnitudes..With this awesome data set, we discovered two
completely new phenomena...who knows what more will be discovered for
the second very-well-observed nova.
"I envision a repeat of the wildly successful U Sco worldwide
collaboration of astronomers, so that we can get very detailed light
curves of T Pyx and all its expected-complicated variations throughout
the eruption. The goal is to follow all the big and subtle variations
in exquisite detail so that we can understand their causes...All
contributing observers will be included as authors of the resulting
papers..."
Coordinates: RA 09 04 41.5 , Dec -32 22 47.4 (J2000.0)
Charts for T Pyx may be plotted using the AAVSO's Variable Star Plotter:
http://www.aavso.org/vsp
Please use the current chart which has the most up-to-date comparison
star magnitudes.
Please promptly submit all observations to the AAVSO International
Database using the name "T PYX".
Thank you in advance for your participation in this very exciting
campaign and for your contributions to this fundamental research!
This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.
-------------------------------------------
SUBMIT OBSERVATIONS TO THE AAVSO
Information on submitting observations to the AAVSO may be found at:
http://www.aavso.org/observing/submit/
Labels: nova, variable star
Wednesday, October 27, 2010
Mira is Brighter!
Image, photo of Cetus taken from my backyard at around 10:45 pm ACDST, the variable star Mira is indicated (Cannon IXUS, 15 seconds at ASA 400). Click to embiggen.I just went out into the back yard and Mira was quite obvious. In a previous post (here, with spotters maps and a magnitude comparison chart) I reported that very early on in the month Mira was already near the brightest it usually gets, and people were predicting a quite bright maximum this year.
My estimate makes it around magnitude 2.5, it is definitly brighter than magnitude 3, but it may have passed maximum brightness while the full Moon was out. I'll definitely be following this star with interest over the next few weeks.
Labels: unaided eye observation, variable star
Wednesday, October 13, 2010
Mira is Bright!
Left hand image, eastern horizon as seen from Adelaide around 10:00 pm ACDST, similar views will be seen elsewhere in Australia at the same local time.Right hand image, photo of Cetus taken from my backyard at around 10:00 pm ACDST, Mira is indicated (Cannon IXUS, 15 seconds at ASA 400). Click to embiggen both.around
Mira is a pulsating Red Giant star that ranges in brightness from under unaided eye visibility to
around magnitude 3-4 in just under a year. This year we were expecting Mira to be around Magnitude 3.7 in late October, but Sky and telescope is reporting that people have been seeing it as bright as magnitude 3.1 already! Mira is fairly low in the sky at reasonable hours, but a few days ago I could confirm that it was bright, at least brighter than magnitude 3.5, but better estimates weren't possible because of light pollution. You can find Mira yourself using the spoter chart above, it's in the smae part of the sky Jupiter, so locating it should be easy.
Magnitude chart for estimating the brightness of Mira.You can have a go at working out how bright Mira is yourself. On this chart I've indicated the magnitude of several comparison stars. You will have to wait until Mira is high enough above the horizon for horizon murk not to interfere (around 11 pm at the moment). Then compare Mira to the reference stars. If it is brighter than the 3.8 star, but dimmer than the 3.5 star, it's magnitude is around 3.6-3.7.
Practice a bit, and keep a record as it nears maximum in late October, then dims again.
Labels: variable star
Thursday, November 26, 2009
No Algol for me....
...or Mercury. Clouds, rain. How did you folks go? For future minima, see the Sky&Telescope minima of Algol page, scroll down to the form that will predict when minima occur in your time zone.
Labels: variable star
Tuesday, November 24, 2009
Algol Blinks, November 25-26
The Northern horizon at 10:00 pm AEDST on November 25 showing the location of Algol.Algol is a classic variable star, but is usually hard to see from the southern hemisphere. This week we have a chance to see Algol dim and brighten under reasonable circumstances. Starting around 11:30 on November 25 Algol will begin to dim, being at its dimmest on the 26th at at 00:30 am AEDST.
It's best to start watching from about 9:30-10 pm AEDST on the 25th, when Algol will still be bright, and over the next few hours you can watch it dim dramatically.
You can determine how far and fast it dims by comparing how bright Algol is to neighbouring stars.
Algol and its neighbours at 11:30 pm AEDST. The numbers indicate the brightness of the stars in magnitude. Algol is magnitude 2.1.To estimate Algols magnitude, compare it to a known brighter stars and known dimmer star. If Algol is dimmer than Almack (2.2) and brighter than the 2.9 stars, it must be around 2.3-2.8.
For more on watching Algol dim and estimating its brightness, see the NHAC Algol project.
For future minima, see the Sky&Telescope minima of Algol page, scroll down to the form that will predict when minima occur in your time zone.
Labels: variable star
Friday, January 09, 2009
What's Up with Polynomial Fits (yes, it has astronomy content)
A reader has wondered why I was so down on polynomial fits in my post on the Australians War Against Science*. Polynomial fits have their place, but to give you an idea of why polynomial fits are a Bad Thing (tm) in climate (or a wide range of) data, without extensive mathematical explanations, have a look at the graph to the left (click to enlarge).The raw data, on casual observation, is a bit noisy, but appears to plateau then fall in the final observations.
The polynomial fit is the green curvy line (I've used a 5th order fit here, as the graph in the Jon Jenkins article used a 5th order polynomial). It sort of wobbles up and down a bit, then does a spectacular dive at the end, just like in the Jenkins graph).
A pretty good estimation of the trend eh? No. The data is actually a continuously increasing line to which I have added noise. The scale of the graph and the range of noise variation was chosen to match the UAH tropospheric temperature data. The "trend" given by the polynomial is dead wrong. The linear fit (black straight line) recovers the real line out of the noise pretty well.
The polynomial fit is quite sensitive to the final data points in a series, it just needs a bit of noise to send the curve flailing around like a snapped hawser. And climate data is very noisy, that's why scientists study long term trends, where the noise can be averaged out. Also, as we are coming off a La Nina event, we expect there to be a drop in global temperatures, it's what La Ninas do. To use a polynomial fit of truncated data when you know there is more data and you know we are coming out of a La Nina event is either sheer stupidity or culpable fraud.
This is why you don't use polynomials fits in these circumstances, they will either be misleading or completely wrong. Have a look at the second graph, it a graph of stellar intensity. The black line is the polynomial fit. Now, if someone told you that the polynomial "trend" meant that the star would soon fade away, would you accept that?
Espeically if you knew it was a truncated section of the intensity graph of Algol? That's the sort of thing Jenkins is trying to get away with.
* They are at it again today, with a headline "Obesity Epidemic a Myth", which grossly distorts the actual science. I'll rant about that later (our kids are nolonger getting exponentially fatter, they are still some of the fattest kids in the world though).
Labels: Climate Change, global warming sillyness, variable star
Friday, December 12, 2008
Speaking of Algol
If you miss out on the minima of Algol, you might like to follow Algol, and other variable stars, using the images from the STEREO spacecraft.Here are an old post where I follow Algol in this way (here) , and you might be interested in this old post, where I make animations of the variable RW Taurii (graphs here)
Labels: Stereo Satellite, variable star
Thursday, December 11, 2008
Algol Blinks
The northern horizon as seen from about Sydney's latitude, at 9:35 pm AEDST on 16 December. The brightness of Algol at maximum and that of surrounding star for comparison are shown in the black and white map. Click on the images to enlarge.Algol is one of the classic variable stars, unlike the red giant Mira which changes brightness through its expansion and contraction, Algol is an eclipsing binary. The bright star has a dimmer companion which passes in front of it just short of every three days causing the star to appear to "blink" (if dimming over 5 hours is a blink). No wonder the stars name means ‘Blinking Demon”.
Algol is very difficult to see from the southern hemisphere, it is below the horizon for a good chunk of the year, and even when it is visible, it is very low to the horizon. This means the times to observe Algol dim are few from the southern hemisphere. However, in the next week there are two good opportunities to see Algol "blink", on the 14th (13th in WA) and 16th of December.
Algols first good minima is on 13:55 Universal Time on the 13th, in Western Australia this is 10:55 pm AWSDST, on the 13th, in Central and eastern Australia this is on the morning of the 14th at 00:25 am ACDST and 00:55 am AEDST. At this time however, Algol is only around a handspan and a half above the northern horizon in Sydney (less in places south, more in places north) , so you will need a fairly level, clear horizon to see Algol (see chart to the left, which if for Sydney at 00:55 am AEDST). In Perth Algol is around two and a half handspans above the horizon and almost due north, so WA folks will have better views. This is the night of the Geminids, so if you are up watching for meteors, you can watch Algol dim and brighten.The next minima is on the 16th at 10:44 UT which is 7: 44 pm AWDST in WA, before sunset. So WA folks miss out. However, in Central and Eastern states it is 9:14 pm ACDST (after civil twilight) and 9:44 pm AEDST (astronomical twilight). The charts for this are at the top of the page. At this time you will miss the dimming, but can easily watch Algol return to brightness.
The total "blink" time (from start of dimming to minimum brightness then back to full brightness) is 10 hours, but you can easily see Algol rapidly change in brightness over an hour or so. At minimum, Algol is as bright as the dim star immediatley above it. You can use the magnitudes shown in the finder chart above to keep track of Algols dimming or rise as outlined in the post about Mira.
So when you are out and about, keep and eye on Algol and you may see it blink!
Labels: variable star
Monday, December 08, 2008
Watching Mira Brighten - Record Your Observations.
The star Mira shines at roughly magnitude 4.2 in this image of the sky taken on 28 November 2008 (click to enlarge, otherwise the stars are a bit to dim to see).While most stars seem to shine with a constant brightness, there are some that undergo regular, dramatic change in brightness. Few of these are visible to the unaided eye, but two classics are Mira and Algol.
Algol is a bit hard for most of us in the southern hemisphere, but Mira is very easy, and Mira (omicron ceti), a star in the constellation of Cetus the whale, is a long period pulsating red giant and changes brightness from below naked eye visibility to a peak of round magnitude 2 (roughly as bright as gamma Crucis in the Southern Cross) in around 330 days. Mira will peak magnitude later this December, and will brighten visibly over this month.
The image above shows Mira on 28 November, when it was around magnitude 4.2, as of last night it was around magnitude 3.9. At the beginning of November I couldn't see it at all, so it was probably magnitude 5.0.Here's a activity for the next few weeks, record the changes in Mira's brightness. This will be difficult for the next few days, as the bright Moon will be nearly on you o f Mira, making the stars hard to see. However, after a few days you will be able to see the stars with reasonable ease.
But I don't know anything about magnitudes, you say. Estimating magnitudes is relatively easy, the image to the left is a chart of Cetus with Miras position marked, and the surrounding stars labelled with their magnitude. To estimate the magnitude of Mira, compare it to the surrounding stars. Is it brighter than a star labelled 3.5, and is it dimmer than a star labelled 3.0? then its magnitude is somewhere around 3.2-3.3.
Click on the chart to enlarge it and print it out. Use a torch with red cellophane wrapped around the business end to view it while star gazing (to keep your night vision), and wait for at least 5 minutes outside for your eyes to dark adapt. Cetus is just above the easily recognized Taurus above the northern horizon in the early evening. This would be an ideal activity for kids.
Labels: kids, Observational Astronomy, variable star
Thursday, April 24, 2008
Lights! Drama! Action! (and RW Taurii)
I realised after posting the RW Taurii light curve, that I should have posted the animation as well. Well, here it is. There is a lot of action and drama in that field. RW Taurii blinks on and off, 17P Holmes slides past the California Nebula (I posted an animation of an earlier section of this event before), 29 Amphrite trundles along, 46 Wiratanen zips past and Ceres proceeds majestically along the bottom. There is even an unknown object (probably an artefact, but my last "artefact" turned out to be 46 Wiratanen).Anyway, the Google Video is below, you can use the image to the right to help identify things (click to enlarge), but it is pretty cheesy. You can download a 1.4 Mb Avi, a 4.5 Mb Avi or a 3.5 Mb gif file which will have more detail. It is better to run the AVI's on a loop a 2x magnification to really get a good handle on the various blobs.
Labels: asteroids, comets, Stereo Satellite, variable star
Wednesday, April 23, 2008
More Fun with Phase Folding
Your probably getting sick of the "Watch Ian painfully learn photometery by trial and error" business, but you might be interested in this phase fold of the Algol type variable RW Taurii. It's around magnitude 8, so far more relevant to exoplanets, even though it has a much deeper eclipse than any exoplanet. I'm still having no luck trying to account for background drift. I've tried another method, averaging intensity over a patch of pixels, but that didn't work. I still have no way to normalize intensity over different STEREO runs.But the field was fantastic, in the stack, you can watch the California Nebula, see Comets Holmes and Wiratannen move across the field, see several asteroids including Ceres and Amphrite, as well as watching RW Taurii blink on and off. Rather nice indeed.
Labels: asteroids, exoplanet, Stereo Satellite, variable star
Sunday, April 20, 2008
Fun with Phase Folding
I'm still trying to figure out how to reduce the variability of intensity measurements in the STEREO Secchi instruments so as to see if I can pick up exoplanet transits. One way is Phase Folding, as used by various groups to study stellar variability. What one does is observe several transits, then alignig all the values with respect to the transit maximum. As the transit maximum will drift, the pints will not align perfectly, so you don't reduce variability per se, but they will define the peak more clearly. Compare the image here, made of 3 passes of Algol phase folded, to the Algol peak defined here on a single pass. Algol is an easy target, but it lest me practise my alignment without hunting for a week trying to find the blasted star. Not also the subsidiary dip. The main dip is when the cool dim star passes in from the the bright star, the subsidiary dip is when the cool dim star is hidden behind the dim star.There's still a few issues. Even for a bright star like Algol, it's measured intensity is quite different between satellite runs, and I have no clear idea of how to normalize this. Also, the more runs you can fold in, the better your sensitivity. However, 83 Leonis has a long period of 17 days, and you only get two passes in STEREO per year. Still, I'll have another go with Phase folding and see what I can come up with.
Labels: exoplanet, Stereo Satellite, variable star
Thursday, March 13, 2008
It's just like having your own cloud-free telescope
As you know, I regularly download images from the STEREO SECCHI imagers to search for comets. I haven't found any yet, but Comet Al has found one or two (or three). But you can see lots more than comets (and coronal mass ejections) in the STEREO images. Like lots of asteroids. As the H1 and H2 instruments only go down to about magnitude 14 at best, you are unlikely to discover any new asteroids though. Nova too, Comet Al caught this image of Nova Scorpii 2007 near comet McNaught in the H2 imager. And variable stars.
The animation above is of the minima of Algol that took place on the 7th of February. Now, this is no big deal for many people, but I have never seen a minima of Algol before (Algol is always too close to my horizon to reliably check it out), so catching it in the STEREO images was something special. Of course, Algol is old hat and well known, but the STEREO images could be used to monitor other less well characterised variables (or at least harder to follow in my scopes). Also, as these at FITS images, you can quantitate the intensity of the star and its drop in magnitude.
Could you use the SECCHI imagers to detect exoplanets? It's a possibility, the exoplanet bearing star has to be relatively bright, lie within the H1 or H2 field of view and have a fairly deep eclipse. WASP-2 and HD 209458 might scrape in under these conditions. HD46375 and HD46375 are within the field of view, fairly bright but have only shallow eclipses. HD2638 is relatively bright (magnitude 9.3), in the field of view of the H1 imager and has a fairly deep eclipse (about 1.2% of total brightness, not to dissimilar to TRES-1's 1.7% fall). Sadly, TRES-1, which has been observed by amateurs, is too far away from the H1 instruments to be imaged.
Still, there is so much out there that is caught in the STEREO imaging cameras, on rainy or cloudy nights it's like having your own personal telescope. Of course, STEREO is a research instrument, actually intended for studying the solar atmosphere, so for us astronomers everything else is gravy. So don't go crazy and download huge chunks of data, think about the researchers who don't need their bandwidth hogged by frenzied amateurs sucking down every last image. Remember, play nice, it's due to them that we get to play with such and awesome instrument for free.
Labels: asteroids, Stereo comet astronomy, variable star
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