Testing the refurbished Leuschner 30-inch telescope and its ability to detect planets around other Stars

Eileen Gonzales, Adam Fries, Adrienne Cool

San Francisco State University

Abstract

Site Characterization

Conclusions and Summary

The 30-inch Ritchey-Chretien telescope at Leuschner Observatory has recently been

refurbished through a collaboration between San Francisco State University (SFSU) and UC

Berkeley. The telescope is equipped with an SBIG STL-11000M CCD and is now being

operated remotely from both campuses. We have carried out observations from SFSU to test

the telescope's performance and to characterize the site in Lafayette, CA. We present the

results of photometric calibrations in B, V and R filters carried out using Landolt standards,

and of the seeing at the site and measured sky brightness in B, V and R filters. Finally, using

observations of the open star cluster M34, we test the accuracy with which we can measure

relative magnitudes, with the goal of using this telescope to detect exoplanet transits.

Seeing

Accuracy of magnitude measurements using M34

Figure 1: Histogram of the V-Filter seeing at

Leuschner. Typical range for seeing between

2.5-3 arcseconds.

Sky Brightness

Figure 5: Sub figures a-d

show the variation in

magnitude for a star of

similar brightness to

WASP-43 for aperture

sizes of 9,11,13,and 15

pixels. The mean

magnitude depends on

aperture size because a

fraction of the star’s flux

lies outside the aperture.

The best aperture size for

the WASP targets was

determined to be 13

pixels.

Figure 2: Sky Brightness in the B, V , and R filters

in magnitudes per square arcseconds.

_____________________________________________________________________________________________________________________________________________________________________

_____________________________________________________

_____________________________________________________ ____________________________________________________________________________________________________________ The goal of accuracy testing was to determine how small of a variation we can detect with the Leuschner telescope, since the transit of an exoplanet reduce the brightness of the host star

between 0.01-1% (http://www.iac.es/proyecto/tep/transitmet.html). If we can detect variations in magnitude at this order, we will be able to detect transiting exoplanets. The immediate goal was

to see of the transits of our targets WASP-43b and WASP-56b were detectable.

Aperture Size Various size apertures were tested on stars in the open cluster M34 to see which one yielded the smallest fluctuations in measured magnitudes for a star similar in brightness to our

exoplanet targets. Apertures of 9, 11, 13, and 15 pixels were tested.

Photometric Calibrations

Figure 4 : A 5-second exposure of M34

taken with the Leuschner Telescope.

____________________________________________________________________________________________________________ Detecting Exoplanet Transits

(a) (b) (c) (d)

Using the results from testing on M34, it was determined that the best apertures size was 13 pixels and that best results were obtained by using a single reference star brighter than the target by

0.2-1.5 magnitudes.

WASP-43b

Figure 6: Relative photometry on 3/22/2014, outside

of transit. Standard deviation of residuals is 0.006

magnitudes.

Figure 10: Relative photometry out of transit,

3/23/2014. Standard deviation of residuals is 0.006

magnitudes.

Figure 8: Relative photometry on 3/24/2014,

during a transit. Standard deviation of residuals

is 0.11 magnitudes, larger than previous nights

due to intermittent cloud coverage.

Date ∆V σ σ of mean

3/22 1.417 0.006 0.001

3/23 1.428 0.007 0.001

3/24 1.450 0.011 0.001

On the first two nights, relative photometry yielded

measurement accuracies of 0.006-0.007 magnitudes for both

targets. On the third night, during the transit windows,

intermittent clouds reduced the accuracy to 0.009-0.011

magnitudes. Nevertheless, we were able to detect a significant

dimming of both targets during transit

In the case of WASP-43, the target was 0.028 magnitudes

fainter during transit than it was on average the two previous

nights. This is consistent with the known transit depth of 0.026

magnitudes (Hellier et al. 2011, A&A, 535, L7), considering the

uncertainty on the difference (σ = 0.014; σ𝑚𝑒𝑎𝑛 = 0.001). For

WASP-56, the target was 0.018 magnitudes fainter during

transit than the previous two nights. Considering the

uncertainties (σ = 0.013; σ𝑚𝑒𝑎𝑛= 0.001), this is also consistent

with the known transit depth of 0.010 magnitudes (Faedi et al.

2013, A&A, 551, A73). Given that the standard deviations of

the mean in both cases are approximately 0.001 magnitudes,

both transits are detected with a high degree of significance.

WASP-56b

Table 1: Comparison of WASP-43

values over 3 nights of observations.

Figure 7: Relative photometry on 3/23/2014,

outside of transit. Standard deviation of residuals

is 0.007 magnitudes.

Figure 9: Relative photometry out of transit,

3/22/2014. Standard deviation of residuals is 0.007

magnitudes.

Figure 11: Relative photometry on 3/24/2014,

during transit. Again intermittent clouds yield larger

standard deviation of residuals than other nights at

0.009 magnitudes

Date ∆V σ σ of mean

3/22 0.167 0.007 0.001

3/23 0.158 0.006 0.001

3/24 0.181 0.009 0.001

Table 2: Comparison of WASP-56

values over 3 nights of observations.

In summary, current techniques allow us to achieve measurement accuracies on the order of 0.006 to 0.007 magnitudes for individual measurements with the Leuschner Telescope. With repeated measurements, this mean that it is indeed possible to detect exoplanet transit with the Leuschner

telescope. To improve the accuracy measurements, we need to determine other methods to use to further lower the detection limit. To increase our confidence in detections, data should be taken before and after the transit.

Photometric calibrations for the B, V, and R filters were determined using Landolt Chart 132.

The Landolt stars were used to determine Leuschner’s zero point, airmass correction, and

color correction.

_____________________________________________________

Filter Z a c Color index

B 21.89 -0.308 0.010 𝑚𝐵 −𝑚𝑉

V 21.65 -0.232 -0.092 𝑚𝐵 −𝑚𝑉

R 21.18 -0.111 -0.17 𝑚𝑉 −𝑚𝑅

Table 1: Photometric calibrations for the Leuschner telescope, as

determined on November 4, 2013

Figure 3 : Landolt Chart 132. The stars used for

calibrations are labeled.

Why Using M34 ____________________________

M34 was used to determine how best to analyze the

transit data for targets WASP-43b and WASP-56b.

It was chosen since it is an uncrowded field with

many stars of constant magnitudes.

We observed WASP-43 and WASP-56 on three nights, with the

last night including a known transit for both targets. To

determine if we detected the transits, we measured magnitudes

for each target relative to a brighter reference star.