Journal Articles by Brad Carter
Mobile learning anytime, anywhere: What are our students doing?
Recent developments in mobile technologies have provided unique opportunities for
learning and te... more Recent developments in mobile technologies have provided unique opportunities for
learning and teaching. This paper reports on recent research undertaken at a regional
Australian university in order to understand how higher education students are using
mobile devices to support their learning. A survey instrument was developed and
deployed and the data collected analysed quantitatively. Upon analysis, these data
demonstrate that students are predominantly using laptop computers to support their
learning, but their use of smart phones and tablets are also used for a number of specific
learning activities. Further analysis indicates that in spite of the limitations in the formal
university infrastructure, many students would like to use their mobile devices for formal
learning as well as informal learning.
Keywords: Mobile learning, m-learning, smart technologies, student usage, higher
education
Papers by Brad Carter
The astrophysical journal, May 3, 2012
We re-analyze 4 years of HARPS spectra of the nearby M1.5 dwarf GJ 667C available through the ESO... more We re-analyze 4 years of HARPS spectra of the nearby M1.5 dwarf GJ 667C available through the ESO public archive. The new radial velocity (RV) measurements were obtained using a new data analysis technique that derives the Doppler measurement and other instrumental effects using a least-squares approach. Combining these new 143 measurements with 41 additional RVs from
Monthly Notices of the Royal Astronomical Society, Jun 2, 2023
Proceedings of the International Astronomical Union, Aug 1, 2013
Doppler Imaging of starspots on young solar analogues is a way to investigate the early history o... more Doppler Imaging of starspots on young solar analogues is a way to investigate the early history of solar magnetic activity by proxy. Doppler images of young G-dwarfs have yielded the presence of large polar spots, extending to moderate latitudes, along with measurements of the surface differential rotation. The differential rotation measurement for one star (RX J0850.1-7554) suggests it is possibly the first example of a young G-type dwarf whose surface rotates as almost a solid body, in marked contrast to the differential rotation of other rapidly rotating young G-dwarfs and the present-day Sun. Overall, our Doppler imaging results show that the young Sun possessed a fundamentally different dynamo to today.
A 7 Day Multiwavelength Flare Campaign on AU Mic. I. High-time-resolution Light Curves and the Thermal Empirical Neupert Effect
The Astrophysical Journal, Jun 29, 2023
We present light curves and flares from a 7 day, multiwavelength observational campaign of AU Mic... more We present light curves and flares from a 7 day, multiwavelength observational campaign of AU Mic, a young and active dM1e star with exoplanets and a debris disk. We report on 73 unique flares between the X-ray to optical data. We use high-time-resolution near-UV (NUV) photometry and soft X-ray (SXR) data from the X-ray Multi-Mirror Mission to study the empirical Neupert effect, which correlates the gradual and impulsive phase flaring emissions. We find that 65% (30 of 46) flares do not follow the Neupert effect, which is 3 times more excursions than seen in solar flares, and propose a four-part Neupert effect classification (Neupert, quasi-Neupert, non-Neupert types I and II) to explain the multiwavelength responses. While the SXR emission generally lags behind the NUV as expected from the chromospheric evaporation flare models, the Neupert effect is more prevalent in larger, more impulsive flares. Preliminary flaring rate analysis with X-ray and U-band data suggests that previously estimated energy ratios hold for a collection of flares observed over the same time period, but not necessarily for an individual, multiwavelength flare. These results imply that one model cannot explain all stellar flares and care should be taken when extrapolating between wavelength regimes. Future work will expand wavelength coverage using radio data to constrain the nonthermal empirical and theoretical Neupert effects to better refine models and bridge the gap between stellar and solar flare physics.
How do Stellar Surveys Like GALAH Improve Our Understanding of Planetary Systems
The time of large-scale astronomical surveys is now upon us. These huge spectral, astrometric and... more The time of large-scale astronomical surveys is now upon us. These huge spectral, astrometric and photometric surveys are providing us astronomers with the richest datasets to date, to better characterise the stars contained within the Milky Way like never before. With almost every star being orbited by at least one exoplanet across our galaxy, these large scale surveys can help better inform us in characterising confirmed and potential planet-hosting stars. We've been able to utilise GALAH's last two data releases (DR2 and DR3), along with GAIA DR2 and EDR3 to better characterise over 125 exoplanet hosts and 250 candidate hosting stars, as well as 45,000 stars currently being observed by TESS. This poster also shows how GALAH's chemical abundances can help inform exoplanetary scientists on what types of planets TESS will likely uncover, and some trends in planetary populations with different chemical abundances.
Monthly Notices of the Royal Astronomical Society, Jan 24, 2018
Based on prior precision photometry and cluster age analysis, the bright star GSC 00154−01819 is ... more Based on prior precision photometry and cluster age analysis, the bright star GSC 00154−01819 is a possible young pre-main sequence member of the Rosette cluster, NGC 2244. As part of a comprehensive study of the large-scale structure of the Rosette and its excitation by the cluster stars, we noted this star as a potential backlight for a probe of the interstellar medium and extinction along the sight line towards a distinctive nebular feature projected on to the cluster centre. New high-resolution spectra of the star were taken with the University College London Echelle Spectrograph of the AAT. They reveal that rather than being a reddened spectral type B or A star within the Mon OB2 association, it is a nearby, largely unreddened, solar twin of spectral type G2V less than 180 Myr old. It is about 219 pc from the Sun with a barycentric radial velocity of +14.35 ± 1.99 km s −1. The spectrum of the Rosette behind it and along this line of sight shows a barycentric radial velocity of +26.0 ± 2.4 km s −1 in H α, and a full width at half-maximum velocity dispersion of 61.94 ± 1.38 km s −1 .
Monthly Notices of the Royal Astronomical Society, Dec 2, 2021
Pioneering photometric, astrometric, and spectroscopic surveys are helping exoplanetary scientist... more Pioneering photometric, astrometric, and spectroscopic surveys are helping exoplanetary scientists better constrain the fundamental properties of stars within our galaxy, and the planets these stars host. In this study, we use the third data release from the stellar spectroscopic GALAH Survey, coupled with astrometric data of eDR3 from the Gaia satellite, and other data from NASA's Exoplanet Archive, to refine our understanding of 279 confirmed and candidate exoplanet host stars and their exoplanets. This homogenously analysed data set comprises 105 confirmed exoplanets, along with 146 K2 candidates, 95 TESS Objects of Interest (TOIs) and 52 Community TOIs (CTOIs). Our analysis significantly shifts several previously (unknown) planet parameters while decreasing the uncertainties for others; Our radius estimates suggest that 35 planet candidates are more likely brown dwarfs or stellar companions due to their new radius values. We are able to refine the radii and masses of WASP-47 e, K2-106 b, and CoRoT-7 b to their most precise values yet, to less than 2.3% and 8.5% respectively. We also use stellar rotational values from GALAH to show that most planet candidates will have mass measurements that will be tough to obtain with current ground-based spectrographs. With GALAH's chemical abundances, we show through chemo-kinematics that there are five planet-hosts that are associated with the galaxy's thick disc, including NGTS-4, K2-183 and K2-337. Finally, we show there is no statistical difference between the chemical properties of hot Neptune and hot rocky exoplanet hosts, with the possibility that short-period rocky worlds might be the remnant cores of hotter, gaseous worlds.
Monthly Notices of the Royal Astronomical Society: Letters, Apr 17, 2019
We report the observation on UT 2017.07.01 of an unusually powerful flare detected in near-infrar... more We report the observation on UT 2017.07.01 of an unusually powerful flare detected in near-infrared continuum photometry of Proxima Centauri. During a campaign monitoring the star for possible exoplanet transits, we identified an increase in Sloan i' flux leading to an observed peak at BJD 2457935.996 that was at least 10% over preflare flux in this band. It was followed by a 2-component rapid decline in the first 100 seconds that became a slower exponential decay with time constant of 1350 seconds. A smaller flare event 1300 seconds after the first added an incremental peak flux increase of 1% of pre-flare flux. Since the onset of the flare was not fully time-resolved at a cadence of 62 seconds, its actual peak value is unknown but greater than the time-average over a single exposure of 20 seconds. The i' band is representative of broad optical and near-IR continuum flux over which the integrated energy of the flare is 100 times the stellar luminosity. This meets the criteria that established the concept of superflares on similar stars. The resulting implied ultraviolet flux and space weather could have had an extreme effect on the atmospheres of planets within the star's otherwise-habitable zone.
Photochemistry and Photobiology, Sep 13, 2012
As part of a wider study into the use of smartphones as solar ultraviolet radiation monitors, thi... more As part of a wider study into the use of smartphones as solar ultraviolet radiation monitors, this article characterizes the ultraviolet A (UVA; 320-400 nm) response of a consumer complementary metal oxide semiconductor (CMOS)-based smartphone image sensor in a controlled laboratory environment. The CMOS image sensor in the camera possesses inherent sensitivity to UVA, and despite the attenuation due to the lens and neutral density and wavelength-specific bandpass filters, the measured relative UVA irradiances relative to the incident irradiances range from 0.0065% at 380 nm to 0.0051% at 340 nm. In addition, the sensor demonstrates a predictable response to low-intensity discrete UVA stimuli that can be modelled using the ratio of recorded digital values to the incident UVA irradiance for a given automatic exposure time, and resulting in measurement errors that are typically less than 5%. Our results support the idea that smartphones can be used for scientific monitoring of UVA radiation.
A Seven-Day Multi-Wavelength Flare Campaign on AU Mic I: High-Time Resolution Light Curves and the Thermal Empirical Neupert Effect
arXiv (Cornell University), Apr 12, 2023
arXiv (Cornell University), Dec 12, 2021
Gliese 86 is a nearby K dwarf hosting a giant planet on a ≈16-day orbit and an outer white dwarf ... more Gliese 86 is a nearby K dwarf hosting a giant planet on a ≈16-day orbit and an outer white dwarf companion on a ≈century-long orbit. In this study we combine radial velocity data (including new measurements spanning more than a decade) with high angular resolution imaging and absolute astrometry from Hipparcos and Gaia to measure the current orbits and masses of both companions. We then simulate the evolution of the Gl 86 system to constrain its primordial orbit when both stars were on the main sequence; the closest approach between the two stars was then about 9 AU. Such a close separation limited the size of the protoplanetary disk of Gl 86 A and dynamically hindered the formation of the giant planet around it. Our measurements of Gl 86 B and Gl 86 Ab's orbits reveal Gl 86 as a system in which giant planet formation took place in a disk truncated at ≈2 AU. Such a disk would be just big enough to harbor the dust mass and total mass needed to assemble Gl 86 Ab's core and envelope, assuming a high disk accretion rate and a low viscosity. Inefficient accretion of the disk onto Gl 86 Ab, however, would require a disk massive enough to approach the Toomre stability limit at its outer truncation radius. The orbital architecture of the Gl 86 system shows that giant planets can form even in severely truncated disks and provides an important benchmark for planet formation theory.
Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Mar 1, 2021
More information: astrophysics.usq.edu.au Overview Cool stars research is central to our studies ... more More information: astrophysics.usq.edu.au Overview Cool stars research is central to our studies of the shared evolution of stars and their planetary systems. These studies are based on international and Australian collaborations and access to observatory facilities including Siding Spring Observatory and Mt Kent Observatory in Australia. Four interrelated themes are shown below. Stellar physics, magnetic activity and winds Key projects: BCool observations of cool star magnetic fields GALAH galactic archaeology with HERMES SONG asteroseismology Modelling the winds of solar-type stars Exoplanet discovery and characterisation Key projects: MINERVA-Australis TESS follow-up spectroscopy Shared Skies Partnership TESS follow-up photometry "Know the star, know the planet"-characterising stars to characterise their planets A stellar-exoplanet connection.
A 7-Day, Multiwavelength Flare Monitoring Campaign on AU Mic
American Astronomical Society Meeting Abstracts #233, 2019
We present the results of multisite observations spanning two years of the pre-main-sequence Herb... more We present the results of multisite observations spanning two years of the pre-main-sequence Herbig Ae star HD 104237. The star was observed in high resolution spectroscopy (R ≥ 35 000) for a total of 157.3 h of effective exposure time, over 42 nights, corresponding to a data base of 1888 individual echelle spectra. We confirm that the HD 104237 system includes a spectroscopic binary, whose primary component HD 104237 A is pulsating. The resulting high quality radial velocity curve allows us to detect for the first time by spectroscopic means multiperiodic oscillations in a pre-main sequence star. Five different modes are detected with very high confidence, with frequencies ranging between 28.5 and 35.6 d −1 , typical of δ Scuti pulsations; an additional 3 frequencies have been extracted from the data, but with a lower level of confidence. The pattern of frequencies indicates that at least some of the detected modes are non-radial. The precise orbit determination and the measurement of the double line spectroscopic binary observed around periastron enabled us to determine a mass ratio of 1.29 ± 0.02 between the primary and the secondary; based on the primary mass of 2.2 ± 0.1 M we conclude that the spectroscopic secondary HD 104237 b should have a mass of 1.7 ± 0.1 M and lie outside the pre-main sequence instability strip towards later spectral types. A search for pulsations in the radial velocity curve of the much weaker secondary component was not conclusive at this stage. The location of the primary in the HR diagram and its position with respect to recent pre-main sequence evolutionary tracks and isochrones implies a location of the secondary indicative of spectral type K3.
Monthly Notices of the Royal Astronomical Society, Apr 1, 2021
The Jovian Trojans are two swarms of small objects that share Jupiter's orbit, clustered around t... more The Jovian Trojans are two swarms of small objects that share Jupiter's orbit, clustered around the leading and trailing Lagrange points, L 4 and L 5. In this work, we investigate the Jovian Trojan population using the technique of astrocladistics, an adaptation of the 'tree of life' approach used in biology. We combine colour data from WISE, SDSS, Gaia DR2, and MOVIS surveys with knowledge of the physical and orbital characteristics of the Trojans, to generate a classification tree composed of clans with distinctive characteristics. We identify 48 clans, indicating groups of objects that possibly share a common origin. Amongst these are several that contain members of the known collisional families, though our work identifies subtleties in that classification that bear future investigation. Our clans are often broken into subclans, and most can be grouped into 10 superclans, reflecting the hierarchical nature of the population. Outcomes from this project include the identification of several high priority objects for additional observations and as well as providing context for the objects to be visited by the forthcoming Lucy mission. Our results demonstrate the ability of astrocladistics to classify multiple large and heterogeneous composite survey data sets into groupings useful for studies of the origins and evolution of our Solar system.
Publications of the Astronomical Society of Australia, May 1, 1996
Zeeman Doppler Imaging (ZDI) is a recent technique for measuring magnetic fields on rapidly rotat... more Zeeman Doppler Imaging (ZDI) is a recent technique for measuring magnetic fields on rapidly rotating, active stars. ZDI employs spectropolarimetry taken at different rotational phases to derive information on the magnetic field distribution over the stellar surface. The Zeeman effect is used to identify the presence of a magnetic field, and variations in Doppler wavelength shifts across the rapidly rotating star allow fields to be resolved on different parts of the visible disk. Analysis of the spectra can be used to produce both thermal and surface magnetic images. ZDI requires very high S/N spectra to be acquired within a time interval short compared to the stellar rotation period. As a result, a large-aperture telescope is needed. Since an initial successful test in 1989, the 3 • 9 m Anglo-Australian Telescope has been used to obtain ZDI spectra of active stars of different evolutionary stages. The observations have concentrated on the K subgiant in the RSCVn system HR1099 to monitor changes on this bright and active star. With the advent in 1991 of ZDI spectropolarimetry with the AAT echelle spectrograph, it has become possible to co-add the polarisation signature from the many magnetically sensitive lines recorded simultaneously. As a result, stellar magnetic field detections of unprecedented quality have been obtained. The aims of this paper are to briefly outline the principles of ZDI, describe the instrumental setup at the AAT and present some preliminary results from recent observations.
Publications of the Astronomical Society of the Pacific, Apr 1, 2013
To understand the frequency, and thus the formation and evolution, of planetary systems like our ... more To understand the frequency, and thus the formation and evolution, of planetary systems like our own solar system, it is critical to detect Jupiter-like planets in Jupiter-like orbits. For long-term radial-velocity monitoring, it is useful to estimate the observational effort required to reliably detect such objects, particularly in light of severe competition for limited telescope time. We perform detailed simulations of observational campaigns, maximizing the realism of the sampling of a set of simulated observations. We then compute the detection limits for each campaign to quantify the effect of increasing the number of observational epochs and varying their time coverage. We show that once there is sufficient time baseline to detect a given orbital period, it becomes less effective to add further time coverage-rather, the detectability of a planet scales roughly as the square root of the number of observations, independently of the number of orbital cycles included in the data string. We also show that no noise floor is reached, with a continuing improvement in detectability at the maximum number of observations N = 500 tested here.
The Astrophysical Journal, May 20, 2002
Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Feb 26, 2021
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Journal Articles by Brad Carter
learning and teaching. This paper reports on recent research undertaken at a regional
Australian university in order to understand how higher education students are using
mobile devices to support their learning. A survey instrument was developed and
deployed and the data collected analysed quantitatively. Upon analysis, these data
demonstrate that students are predominantly using laptop computers to support their
learning, but their use of smart phones and tablets are also used for a number of specific
learning activities. Further analysis indicates that in spite of the limitations in the formal
university infrastructure, many students would like to use their mobile devices for formal
learning as well as informal learning.
Keywords: Mobile learning, m-learning, smart technologies, student usage, higher
education
Papers by Brad Carter
learning and teaching. This paper reports on recent research undertaken at a regional
Australian university in order to understand how higher education students are using
mobile devices to support their learning. A survey instrument was developed and
deployed and the data collected analysed quantitatively. Upon analysis, these data
demonstrate that students are predominantly using laptop computers to support their
learning, but their use of smart phones and tablets are also used for a number of specific
learning activities. Further analysis indicates that in spite of the limitations in the formal
university infrastructure, many students would like to use their mobile devices for formal
learning as well as informal learning.
Keywords: Mobile learning, m-learning, smart technologies, student usage, higher
education