Salam Dulaimi

Brown dwarfs and low-mass stars together comprise the group of galactic objects known as ultracool dwarfs. A number have been detected as radio sources – in some cases, emitting periodic radio pulses synchronised to the dwarf's known rotational period. Detections of optical variability in ultracool dwarfs have been primarily attributed to stellar rotation, with the modulations observed a consequence of either magnetic spots on the surface, the presence of atmospheric dust, or auroral emission. A combination of these mechanisms may be required to explain some dwarf lightcurves. Rotational estimates of ultracool dwarfs are typically obtained spectroscopically; however accurate estimates of true rotation velocities require knowledge of the dwarf's rotational inclination axes. Direct measurement of a rotational signature in photometric data however provides an unambiguous rotational period, and this information can be used to constrain dwarf inclination geometries. In this thesis, we report on over ~ 160 hrs monitoring in I-band of multiple epochs from four ultracool dwarfs, spanning M tight binary dwarf 2MASS J1314203+132001A and L tight binary dwarf 2MASS J0746425+200032AB, the M9.5 dwarf BRI 0021-0214, and the L3.5 dwarf 2MASS J00361617+18211. This photometric campaign was carried out using the Galway Ultra-Fast Imager (GUFI) on the 1.8m Vatican Advanced Technology Telescope (VATT), on Mt. Graham, Arizona. All selected dwarfs exhibit periodic optical variability, where periods of both secondary components for our binary samples were newly discovered. This thesis discusses the use of two photometric analysis tools with the explicit aim of improving the quality of ground-based photometric measurements. Each data set was used to test the performance of the two systems. We find the LuckyPhot technique has obvious benefits to high precision photometry by reducing photometric errors, where the mean RMS error was reduced by ~ 47% with respect to the errors produced by the more standard GUFI pipeline method. This thesis also outlines a novel tool, Light Curve Fitter, which we apply to the binaries to investigate the presence of periodic photometric modulation in both binary members: refining the dominant member variability parameters, and searching for an elusive period of the weaker member. Light Curve Fitter is a python-based program, capable of detecting superposition of two sinusoidal waves to untangle the weaker components variability signature from that of the dominant source variability. We identify a newly discovered optical variability in the primary and secondary components of ultracool dwarf binary 2MASS J1314203+132001AB and 2MASS J0746425+200032AB, respectively. The optical data presented for both systems shows strongly correlated emissions in terms of phase and temporal variability. We have also shown the A and B variability signals of both dwarf binaries 2MASS J0746425+200032AB and 2MASS J1314203+132001AB, respectively, to be extremely consistent and stable over multiple epochs. This stability had seen in both radio and spectroscopic data, and the mechanism driving these processes in different parts of the electromagnetic spectrum could perhaps be fundamentally linked. We also investigate the orbital coplanarity of both binary dwarfs. Here the ability to deconvolve the inclination angle from the spectroscopic radial velocities, using direct estimates of the dwarf rotational periods, allows us to constrain the spin-orbit coupling of the binary system. In the case of the L dwarf binary 2MASS J0746425+200032AB, we calculate the equatorial inclination angle of the binary rotation axes are in alignment with the orbital plane of the system to within 10 degrees, consistent with solar-type binary formation mechanisms. For the M7 dwarf binary 2MASS J1314203+132001AB, due to missing parameters for the primary component, we investigate a tentative alignment of the spin-orbital axes of the A component. We find that the equatorial inclination angle of the secondary member spin axes is largely consistent with being aligned perpendicularly to the orbital plane. Finally, we find the rotation axes of the two single dwarfs are not perpendicular to our line of sight.

Kindly funded by the Outline for the Lucky Phot technique. This figure was taken from Nail & smith 2013 VATT Telescope 2MASSW J0746425+200032AB GUFI mk. II is a portable L3-CCD photometer which was designed specifically for variable star observations that requires second to sub-second timescales. The system uses the Andor iXon DV887 EM-CCD camera, which has a CCD97 sensor with 512 x 512 format and > 90% quantum efficiency. It offers up to 10 MHZ pixel readout rate and can operate from 32-526 frames per second, at a duty cycle approaching~100%. It is currently stationed at the 1.8m VATT telescope in Arizona, with a FOV of 3' x 3'. We used an I-band broadband filter for observations over the course of three separate epochs (Mar, Nov, Dec 2017), for a total of ∼140 hr. 2M J0746AB is an L dwarf binary (L0 + L1.5) with a separation of ∼2.7 AU (Reid et al. 2001), located at a distance of 12.20 ± 0.05 pc (Dahn et al. 2002). Harding et al. (2013) reported a period of 3.32 ± 0.15 hr for 2M J0746A, whereas Berger et al. (2009) detected the secondary 2M J0746B with a period of 2.07 ± 0.002 hr in 4.86 GHz radio, as well as quasisinusoidal Hα emission with the same period. Thus far, no periodic optical variability has been detected for 2M J0746B. Therefore, we chose to monitor the binary to investigate the presence of optical variability in the secondary component, and to determine whether the optical variability of the primary 2M J0746A was stable over timescales of years.

In 2013, Harding et al. investigated the optical signatures from magnetospheric phenomena in stars at the end of the main sequence, and for stars below the substellar boundary (late-M/early-L dwarfs). They commissioned the Galway Ultra-Fast Imager (GUFI) Mark II in 2009 on the VATT in Arizona, to establish the correlation, if any, between the optical and radio regimes, for six radio detected ultracool dwarfs, including two binary systems. They found periodic variability in five of these dwarfs. The sixth (BRI 0021) showed persistent variability, without a definite periodicity. In order to better understand this variability , we are going to use a technique called Lucky Photometry (Collins & Smith, 2013) to lower the light curve scatter. Additional time has also been secured for a new GUFI campaign on the VATT. The combination of old (re-analysed) and new data, processed with the new technique, will allow us to improve light curve solutions and to investigate secular stability of these periods, amplitudes and phases. Moreover, we will try to: search for superimposed aperiodic components; decouple short-lived dust effects from enduring auroral ones; remove the uncertainty around the possible periodicity of BRI 0021; and find the elusive secondary periods in the two binaries.

2MASS J13142039+1320011 (hereafter 2M J1314AB) is an ultracool
dwarf binary system of spectral type M7, with a separation of∼1.6
AU. This system outputs the highest X-ray and radio luminosities
detected from an ultracool dwarf to date, due to its extreme levels of
magnetic activity. Several studies of 2M J1314AB have revealed
clear, sinusoidal photometric variability in several optical filters with a
period of 3.79 hr, in good agreement with its 3.89 hr radio periodicity.
The measured periods in both radio and optical have been attributed
to the rotation of the primary component of the binary. Here, we
present optical photometry of 2MJ1314AB over a period of ∼1.3 yr,
encompassing three separate epochs, obtained with the Galway
Ultra-Fast Imager (GUFI) on the 1.8m Vatican Advanced Technology
Telescope (VATT),on Mt. Graham, Arizona. We obtained ~50 hr of
monitoring in I-band, to search for optical variability in the secondary
component, and to determine whether the optical variability of the
primary component was stable over timescales of years. The data
was reduced by our in-house GUFI Pipeline, and a Python code,
capable of detecting the superposition of two sinusoidal waves, was
written to untangle the secondary component’s variability signature
from that of the dominant primary variability. All three epochs yielded
a rotation period of ~ 3.79 hr from primary component, with an
amplitude of ~ 0.02 magnitude, consistent with previous studies. The
results indicate that we discovered the secondary rotation period ~
2.05 hrs. Our results add further weight to a likely association
between the source of optical and radio periodic variability in late-M
dwarfs. However, at this point, the underlying physical cause of such
a possible connection remains ambiguous.

GUFI mk. II is a portable L3-CCD photometer which was designed specifically for variable star observations that requires second to sub-second timescales. The system uses the Andor iXon DV887 EM-CCD camera, which has a CCD97 sensor with 512 x 512 format and > 90% quantum efficiency. It offers up to 10 MHZ pixel readout rate and can operate from 32-526 frames per second, at a duty cycle approaching~100%. It is currently stationed at the 1.8m VATT telescope in Arizona, with a FOV of 3' x 3'. We used an I-band (∼ 7200-9100 Å) broadband filter for observations over the course of two separate epochs (October and December 2017), for a total of ∼ 19 hours.

The Galway Ultra-Fast Imager (GUFI) located on the 1.8m Vatican Advanced Technology Telescope (VATT) was tasked to monitor tight brown dwarf binaries. However, due to the close separation between the components in these binaries, the GUFI photometer could not image each component of binary systems as a point source in our campaign. Therefore, we developed and employed our novel application, the 'Light Curve Fitter', which is capable of distinguishing two superimposed sinusoidal waves. This application allows users to untangle the secondary component's variability signature from that of the dominant primary variability.

We report I-band photometric observations of the radio-detected M9.5 dwarf BRI 0021−0214, obtained with the Galway Ultra Fast Imager on the 1.8 m Vatican Advanced Technology Telescope (VATT) at Mt. Graham International Observatory, Arizona. In total, 19 h of observations over a 73 d baseline were obtained. BRI 0021−0214 was shown to exhibit modulated emission with a period of 3.052 ± 0.004 h with a mean amplitude variability of 0.0044 mag. When combined with rotational velocity data obtained from previous work, our newly discovered rotation period gives an inclination angle of 51.7$^{+5.0}_{-4.5}$ deg for the rotation axis of BRI 0021-0214 relative to our line of sight. Previous studies have reported that the most plausible cause for optical variability from this dwarf is a consequence of suspended co-rotating dust clouds in its atmosphere. However, reports of enhanced Hα and intermittent coherent radio emission suggest the possibility of auroral activity in its magnetosphere. Furth...