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1
Visual Variable Star Observing Is Fun
What I’ve Been Doing And What You Could Do Too
Ben Mullin
2
Why Am I Here
• Talk about how much fun I’ve been having visual variable star observing (VSO)
• Basics of VSO and how you could get involved• What you can observe
– including some variables close to objects you probably already observe
• How VSO has improved my observing• What the data you collect might mean• Not going to be a technical talk (I’m not an expert)
– A little math can add to the fun
3
My Road To VSO
• Always known VSO was an option• Deep Space Objects are cool• What could be fun about observing a single
star?• Imaging is also fun• Eventually I got interested in the
processing, plotting, and analyzing aspects of CCD VSO
4
My Road Continued
• Theoretically I have all of the equipment necessary to do CCD VSO
• Prime focus imaging with a narrow field of view is really hard
• So VSO sat on the back burner while I worked on getting things together
• Somehow decided visual observations would be too difficult
5
My First Observation
• Realized that it was still going to be a while before I got CCD all sorted out
• I knew Algol was a regular eclipsing binary that was pretty easy to observe
• Started with the American Association of Variable Star Observers (AAVSO) Manual for Visual Observing of Variable Stars
• This gave the basics on how to make an observation.
6
Observing Algol
• First step is to know when the eclipse is expected– Published in S&T also an
applet on the S&T website
• Get a chart from the AAVSO with comparison stars
7
8
My Observations
• In and out of the house while getting the kids ready for bed (did I mention STI?)
• 8 observations over 3.5 hours
Algol 9/28/2007
2
2.2
2.4
2.6
2.8
3
3.2
3.4
2454372.55 2454372.6 2454372.65 2454372.7 2454372.75
J ulian Date
9
Global Collaboration
• Looks like I missed the minimum
• But, what about collaborating with others?
• Between me and Stanislaw Swierczynski from Poland we captured the minimum.
Algol 9/28/2007
2
2.2
2.4
2.6
2.8
3
3.2
3.4
2E+06 2E+06 2E+06 2E+06 2E+06 2E+06
Julian DateM
agn
itu
de My Observations
StanislawSw ierczynski, Poland
10
Historical Data
• How does this compare to historical AAVSO data?
Phase Plot of Beta Per
1.5
2
2.5
3
3.5
4
4.5
0 0.2 0.4 0.6 0.8 1
Phase
Ma
g
AAVSO Data
Observation Set 1
Observation Set 2
11
Wasn’t That Fun?
• Collected real data on an astronomical event• Collaborated with another observer on
another continent• Made cool graphs and had data to play with
when it was cloudy• Increased my observing skills• Any excuse to go out and look up is a good
one
12
So How Did I Do That?
• Already mentioned the Manual for Visual Observing, eclipse predictions, and chart
• What about the actual observations?
• Is it hard?
• It’s easy and you can learn to do it in just a few minutes.
13
Making Estimates
• Making estimates
14
Told You So!
• Pretty easy isn’t it
• Other things to consider– Avoid biasing your estimate– Report what you see– Don’t stare at red stars– Number one source of error is mis-
identification of the variable
15
Now What?
• Register as an AAVSO observer
• It’s easy and free
• Report your estimate
• Your estimates could be used by professional astronomers doing cutting edge research
16
What You Need To Report An Observation
• Your observer initials (free registration with the AAVSO)
• Designation or name of the star observed
• Your estimate
• The chart used
• The comparison stars used
• Julian date of the observation
17
Online Submission
18
Putting It All Together
• Pick a star
• Get a chart from the AAVSO
• Make and record your observation
• Register as an AAVSO observer
• Report your observation
19
See Your Contribution To Science
20
What Could You Observe?
• A very brief overview of variable star types and their representative light curves– Not a strength of mine yet
• Interesting/easy variables you could try
21
Broad Categorization
• Intrinsic– Pulsating– Cataclysmic
• Extrinsic– Eclipsing– Rotating
22
Pulsating
• Cepheid – 1 to 70 days, 0.1 to 2.0 mags• RR Lyrae – 0.05 to 1.2 days, 0.3 to 2.0 mags• RV Tauri – 30 to 150 days, up to 3 mags,
alternating deep/shallow minimum• Long Period Variables (LPV) – 30 to 1000 days
– Mira – 80 to 1000 days, more than 2.5 mags– Semiregular – 30 to 1000 days, less than 2.5 mags,
intervals of semi or irregular variation
• Irregular
23
Cepheid Light Curve
24
RR Lyrae Light Curve
From Koppelman, Huziak, Cooney, Petriew
25
Mira Light Curve
26
Semiregular Light Curve
27
Cataclysmic• Super Novae – One in Antennae Galaxy announced
12/19/2007, or M51 a few years ago• Novae – One in Puppis announced in November, one in
Vulpecula in December• Recurrent Novae• Dwarf Novae
– U Gem – Periods of quiescence then erupt– Z Cam – Like U Gem, but with “standstills”– SU UMa – Like U Gem, but with regular outbursts and super-
outbursts
• Symbiotic stars – Close binary systems• R CrB – Dwarf novae in reverse
28
Super Novae Light Curve
29
Novae Light Curve
30
Recurrent Novae Light Curve
31
U Gem Light Curve
32
Z Cam Light Curve
33
SU UMa Light Curve
34
R CrB Light Curve
35
Variables You Might Observe
• Noteworthy
• Easy
• Near other commonly observed objects
• Interesting
• We already talked about Algol
36
Omi Cet - Mira
• Maximum predicted near Feb 3, 2008
• Going to become naked eye quickly
37
38
Delta Cep
• Bright
• Only a 5 day period
39
40
Zeta Gem
41
Zeta Gem
• Cepheid
• Period 10.15 days
• Magnitude range 3.62-4.18
• Easy to find, hard to estimate
42
M31/RX And
43
RX And
• UGZ• Z Cam• Very Active• Outbursts and
standstills• Magnitude range 10.3-
14.0
44
45
M42/S Ori
46
S Ori
• Mira• Period 419 days• Magnitude range 8.4-
12.9• Also a double star
47
48
M81/M82/R UMa
49
R UMa
• Mira• Period 301 days• Magnitude range 6.6-
14.3
50
51
Double Cluster/S Per
52
S Per
• SRC• Period 822 days• Magnitude range 7.9-
12.
53
54
RZ Cas
55
RZ Cas
• Eclipsing binary• 4 hours to complete
cycle• Binocular object
56
57
How VSO Has Helped My Observing
• Admittedly not an advanced observer to begin with
• Star hopping• Averted vision• Contrast, magnification, and eyepieces• Concentration• Most importantly it has added a fun purpose
to my observing
58
Are Math and Astrophysics Fun?
• They certainly can be
• Let’s see what my 19 observations of X Cyg can tell us
59
Cepheid Variables
• A class of variable stars• Prototype star is Delta Cepheid discovered
in 1784 by John Goodricke• Henriette Leavitt discovered that their
period is closely correlated to their absolute magnitude
• Can be used as a standard candle to measure astronomical distances
60
X Cyg is a Cepheid
• So if we can determine the period we can determine the absolute magnitude of the star
• Arne Henden, AAVSO director, pointed me to a primer paper, “Time-Series Analysis of Variable Star Data” by Matthew Templeton published in the Journal of the AAVSO
• Among other techniques, it described the ANOVA (analysis of variance) method for determining the period
61
My Data
• 19 Observations over 5 cycles in 72 days
My X Cyg Observed Magnitudes
5.8
6
6.2
6.4
6.6
6.8
7
7.2
2454370 2454385 2454400 2454415 2454430 2454445 2454460
Julian Date
Mag
nit
ud
e
X Cyg
62
ANOVA Analysis• My 19 points versus all 20000+ AAVSO
points
• My 16.36 days versus all AAVSO 16.3859 days versus reported 16.386332 days
0
0.5
1
1.5
2
2.5
3
14 15 16 17 18
Analysis of All AAVSO Data
Analysis of My Data
63
Period-Luminosity Relationship
• We have determined the period, we can now calculate the absolute magnitude
• Period-Luminosity relationshipMv = -3.141*Log(P)-.826
• Mv = -3.141*Log(16.36)-.826 = -4.674 mag
• Now we know how bright it actually is and we know how bright we see it as…
64
Magnitude Equation
• m - Mv - Av*d/1000 = 5*log(d/10)• m is the observed magnitude (average) – 6.38• Mv is the absolute magnitude - -4.674• d is the distance in parsecs - unknown• Av is extinction in mags/kparsec – 2.8 mags/kpc• Use Excel’s Goal-Seek function to find d• d = 716.68pc = 2339ly
65
Compare That To The Professionals
• ESA Hipparcos satellite measured the parallax of many stars including X Cyg
• 1.47 +/- 0.72 milli arcseconds annual parallax for X Cyg
• d = 1000/mas• 456pc-1333pc “centered” at 680pc• 680pc compared to 716pc, not too shabby
for a set of binoculars!
66
Almost Treat Time
• I have been having more fun observing than ever
• Possibly contributing to science
• Improving my observing skills
• Adds some fun things to do on cloudy nights
67
Thank You