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Visual Variable Star Observing Is Fun

What I’ve Been Doing And What You Could Do Too

Ben Mullin

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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

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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

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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

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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.

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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

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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

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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

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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

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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

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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

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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

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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.

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Making Estimates

• Making estimates

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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

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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

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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

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Online Submission

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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

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See Your Contribution To Science

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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

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Broad Categorization

• Intrinsic– Pulsating– Cataclysmic

• Extrinsic– Eclipsing– Rotating

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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

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Cepheid Light Curve

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RR Lyrae Light Curve

From Koppelman, Huziak, Cooney, Petriew

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Mira Light Curve

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Semiregular Light Curve

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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

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Super Novae Light Curve

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Novae Light Curve

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Recurrent Novae Light Curve

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U Gem Light Curve

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Z Cam Light Curve

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SU UMa Light Curve

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R CrB Light Curve

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Variables You Might Observe

• Noteworthy

• Easy

• Near other commonly observed objects

• Interesting

• We already talked about Algol

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Omi Cet - Mira

• Maximum predicted near Feb 3, 2008

• Going to become naked eye quickly

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Delta Cep

• Bright

• Only a 5 day period

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Zeta Gem

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Zeta Gem

• Cepheid

• Period 10.15 days

• Magnitude range 3.62-4.18

• Easy to find, hard to estimate

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M31/RX And

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RX And

• UGZ• Z Cam• Very Active• Outbursts and

standstills• Magnitude range 10.3-

14.0

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M42/S Ori

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S Ori

• Mira• Period 419 days• Magnitude range 8.4-

12.9• Also a double star

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M81/M82/R UMa

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R UMa

• Mira• Period 301 days• Magnitude range 6.6-

14.3

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Double Cluster/S Per

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S Per

• SRC• Period 822 days• Magnitude range 7.9-

12.

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RZ Cas

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RZ Cas

• Eclipsing binary• 4 hours to complete

cycle• Binocular object

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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

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Are Math and Astrophysics Fun?

• They certainly can be

• Let’s see what my 19 observations of X Cyg can tell us

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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

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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

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My Data

• 19 Observations over 5 cycles in 72 days

My X Cyg Observed Magnitudes

5.8

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6.2

6.4

6.6

6.8

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7.2

2454370 2454385 2454400 2454415 2454430 2454445 2454460

Julian Date

Mag

nit

ud

e

X Cyg

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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

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1

1.5

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2.5

3

14 15 16 17 18

Analysis of All AAVSO Data

Analysis of My Data

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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…

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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

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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!

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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

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Thank You