Photometry of V407 Vul and RX J0806'3 1527

1
Photometry of V407 Vul and RX J0806.31527
Susana Cristina Cabral de Barros Astronomy and
Astrophysics Group, University Warwick

• Outline
• Origin of optical emission
• Photometry Results
• V407 Vul Position studies
• Irradiation?

2
Optical emission
Marsh Steeghs, Ramsay 2002
Wu et al 2002
3
Observations
4,2 m WHT, La Palma with the high speed CCD
camera ULTRACAM with simultaneous bands I, g
and u.

• Observations
• V407 Vul 21-25 May 2003
• 3600 frames of 9,7 sec exposure
• RX J0806 20-25 of May 2003
• 2000 frames of 10.1 sec exposure

4
V407 Vul Phase-Folded Light Curves
Normalised semi- amplitudes u 20.5 g
8.71 i 3.01

• Ephemeris from Strohmayer (2004)

5
Phase Shift in V407 Vul

• Phases of maximum flux For V407 Vul the phases
  show a progressive delay with shorter wavelengths
  that is expected from a region downstream of a
  direct impact (as predited by Hakala et al 2004).
• u 0.0133 /- 0.0041
• g 0.0075 /- 0.0015
• i 0.0000 /- 0.0024
• (orbital cycles)

6
RX J0806 Phase-Folded Light Curves
Normalised semi-amplitudes u 13.4 g
13.6 i 14.8

• Ephemeris from Strohmayer (2005)

7
RX J0806 Optical Phase relative to the X-rays

• Israel et al. (2004, MnSAI)

8
Compare the systems
V407 Vul
RX J0806

• Phase of the maximum in optical is at 0.2 i.e.
  0.2 before the X-ray maximum and 0.3 before the
  X-rays mean.

• Phase of the maximum in optical is at 0.15 i.e.
  0.20 before the X-rays maximum and 0.35 before
  the X-rays mean.

9
Position Studies

• V407 Vul is observed to have the spectrum of a G
  star. We test whether this could be a
  line-of-sight coincidence.
• If the G star is separated from V407 Vul on the
  sky, we would expect to see a variation in the
  position of V407 Vul on its 569 sec pulsation
  period.

Xc - 0.20
Xc - 0.64
10
Pulsation Astrometry

• We only obtain a significant detection for the g
  band in the Y position.
• This peak is formally significant at a level of
  99.9 percentile,
• We phase folded the Y position of the g band and
  obtain a semi-amplitude of 0.01 pixels equivalent
  to 0.04 to 0.07 arcsec.

11
Real detection?

• The constant star would be at the top of V407 Vul
• The problem is that V407 Vul is in a crowed
  field.
• The i is the most affected band, but g could
  also be affected and we could be seeing a signal
  due to other stars.
• Filtering the worse seeing points increases the
  signal.
• There is no correlation between the position and
  the seeing after the filtering.
• We need better data to be sure of our detection.

i
g
12
Irradiation Studies

• We used reasonable system parameters to simulate
  the optical light curve of V407 Vul and RX J0806
  produced by irradiation.
• The parameter that most affects the shape of the
  light curve is the orbital inclination.
• For low inclination systems the signal is a
  perfect sinusoid.
• For high inclination systems the second harmonic
  is relative important.

13
Conclusions

• We have a hint of a phase-shift of the optical
  light curves of V407 Vul supporting the direct
  impact model.
• We revise the phase shift between optical and
  X-ray light curves of RX J0806 which makes it
  look very similar to V407 Vul.
• We have a hint of a detection of a spatial
  separation of the G star in V407 Vul.
• If the optical light comes from irradiation of
  the secondary the inclination of V407 Vul is 30
  º/- 10 º and RX J0806 is 70º /-10º

SCC Barros is supported by Fundação para a
Ciência e Tecnologia