DSLR Photometry Highlights Mark Blackford Outline 1 DSLR

DSLR Photometry Highlights Mark Blackford

Outline 1. DSLR Photometry outline 2. E 1 Region standard stars 3. Camera problem? 4. η (eta) Muscae eclipsing binary 5. KX Velorum eclipsing binary 6. HD 92607 a new variable? 7. GG Lupi eclipsing binary 8. Conclusions

www. aavso. org/dslr-observing-manual

DSLR Photometry Summary Benefits: – Simultaneous RGB (transform to BVRc) – Don’t need filter wheel and filters – Wide field of view (several target and comparison stars) – Relatively cheap Drawbacks: – 14 bit ADC (12 bit for older models) – Non-photometric filters – Image must be defocused – Small image scale (close stars overlap in images)

DSLR Photometry Summary Equipment: – Basic Canon DSLR body (APS-C sensor) – Medium fixed focal length telephoto lenses – 80 mm f 6 refractor – Computer controlled GOTO equatorial mount – The. Sky. X, Backyard EOS, Dimension 4, Max. Im DL Analysis: – AIP 4 Win, Muniwin, Max. Im DL – Bespoke Excel spreadsheets (data reduction, To. M) – Peranso, VStar

Key Points • DSLR photometry can be accurate and precise • Transformation of instrumental RGB magnitudes is possible for normal stars with approximately black-body spectra • Instrumental magnitudes of stars with strong emission and/or absorption features cannot be reliably transformed (e. g. novae, supernovae) • Useful measurements can still be made of these stars, e. g. time of minimum or maximum light, pulsation period

E 1 Region Transformed Magnitudes delta = measured magnitude minus catalogue magnitude

Canon 450 D + Nikkor 180 mm f 2. 8 lens Celestron 8” Edge. HD Celestron CGEM mount Canon 600 D + Canon 200 mm f 2. 8 lens

Camera Problem? Obvious conclusion: Logical solution: Canon 600 D is faulty buy new DSLR (Canon 1100 D)

What’s Really Going On Here? Insufficient De-Focus! Star centroid position over 55 minute time series Periodic error and drift Centroid sometimes on a red pixel, sometimes blue or green Very little intensity in surrounding pixels

Sufficient De-Focus Adequate sampling of all three colours Avoid saturation of bright stars Increase total photon count by increasing exposure time

η Muscae Multiple star system with at least 5 components: • η Mus A, eclipsing binary (Aa and Ab), 4. 66 - 4. 74 V mag, 2. 3963 d period • η Mus B, 58 arcsec, 7. 3 V mag, ~200, 000 year orbit • η Mus C, 3 arcsec, 10 J mag, ~3, 000 year orbit • η Mus D, ~5. 5 year orbit inferred from radial velocity measurements after accounting for radial velocity changes due to orbit of η Mus A

η Muscae (E. Budding, R. Butland M. Blackford (2013), PASA, 30, e 037 doi: 10. 1017/pasa. 2013. 15) This is also detectable as variation of eclipse times of minimum

Light Travel Time Effect (LITE) Observer D Aa Ab ~2. 4 day orbit X ~5. 5 year orbit NOT TO SCALE Stars B and C much further away

Light Travel Time Effect (LITE) Observer D X Aa Extra distance due to orbit of η Mus A around the center of gravity with η Mus D Ab

Canon 1100 D + Canon 200 mm f 2. 8 lens Canon 600 D + Orion ED 80 T CF f 6 Celestron CGEM mount

η Mus image

2014 & 2016 V light curves Green: May 2014 Red: Feb 2016

Observed – Calculated (O-C) Diagram

O-C Diagram Refinement of star D orbit is required (period, ellipticity, inclination)

Pavel Mayer, Charles University in Prague, Czech Republic KX Velorum EA eclipsing binary with an evolved early type component V magnitude 5. 10 26. 30575 day period Only previously observed eclipse was 1986 More photometry and spectroscopy required to better determine masses, radii, temperatures, etc. P. Mayer, H. Drechsel, and A. Irrgang, Astron. Astrophys. 565, 86 (2014)

KX Velorum January 2015, 7 hr 45 min time series

KX Velorum Looks like bottom of eclipse was observed

Portable Rig Canon 1100 D + Canon 200 mm f 2. 8 lens i. Optron ZEQ 25 mount

HD 92607 Selected as potential comparison star for QZ Car, however it soon became clear that it was not constant. Not in the General Catalog of Variable Stars (GCVS) The SIMBAD database lists it as a non-variable star with spectral type O 9 II/III. A search of AAVSO Variable Star Index for variables near RA and Dec of HD 92607 showed that the star was found to be variable by the All Sky Automated Survey (ASAS) in I band. Classified as an eclipsing binary with 1. 29593 day period.

HD 92607 Eta Car HD 92607 QZ Car

HD 92607 ASAS-3 V Light Curve

Less scatter, primary ~0. 01 mag deeper, slight O’Connell effect

B and R data acquired simultaneously, although somewhat noisier

GG Lupi • Absolute Parameters of Young Stars: GG Lup and μ 1 Sco, E. Budding, R. Butland, M. Blackford, MNRAS, Volume 448, Issue 4, p. 3784 -3796 • EB type detached eclipsing binary • Magnitude range 5. 56 – 6. 19 V • Period 1. 84960 days • Elliptical orbit with eccentricity ~0. 15 • Period of apsidal motion ~100 years

Apsidal motion The precession of the periastron of a binary system resulting from tidal gravitational moments.

Observer A B Time from primary eclipse to secondary eclipse is the same as time from secondary eclipse to primary eclipse

Time from primary eclipse to secondary eclipse NOT the same as time from secondary eclipse to primary eclipse Observer B A

GG Lupi 1985 Strömgren y light curve (J. Andersen, J. V. Clausen, and A. Gimenez, Astron. Astrophys. 277, 439 -451 (1993)) Secondary at phase 0. 5, Primary 8. 8% of light curve, secondary 12. 6%

GG Lupi 2012 DSLR light curves (Absolute parameters of young stars: GG Lup and μ 1 Sco, MNRAS (April 21, 2015) 448 (4): 3784 -3796. ) Secondary at phase 0. 4, Primary 10. 3% of light curve, secondary 10. 3%

2012 & 2014 V light curves Green: May 2012 Red: July 2014

O-C diagram Petr Zasche, Charles University in Prague, Czech Republic JD 0 = 2446136. 744 (± 0. 016) HJD Period = 1. 8496002 (± 0. 0000051) days (Sidereal) Period = 1. 8496900 (± 0. 0000051) days (Anomalistic) Ellipticity = 0. 157 (± 0. 046), Apsidal period = 104. 3 (± ? ) More observations every couple of years

Canon 1100 D + Canon 200 mm f 2. 8 lens Canon 600 D + Orion ED 80 T CF f 6 Celestron 8” Edge. HD Soon to be equipped with a CCD and filter wheel Paramount MX+

All observing so far from here

Soon from here

Conclusions • DSLR photometry can be both accurate and precise • Targets with strong emission or absorption spectra are not suitable for transformed magnitudes but useful observations are still possible (e. g. novae and supernovae, period analysis, times of minimum or maximum) • Amateurs with modest equipment can photometrically monitor stars that are too bright for professional telescopes • Pro-Am collaborations can be very rewarding