Siding Spring Research Articles

Probing the physics of narrow-line regions of Seyfert galaxies

We have used the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope at Siding Spring to observe the nearby, nearly face-on, Seyfert 2 galaxy, NGC 5427. We have obtained integral field spectroscopy of both the nuclear regions and the HII regions in the spiral arms. We have constrained the chemical abundance in the interstellar medium of the extended narrow line region (ENLR) by measuring the abundance gradient in the circum-nuclear \ion{H}{ii} regions to determine the nuclear chemical abundances, and to use these to in turn determine the EUV spectral energy distribution for comparison with theoretical models. We find a very high nuclear abundance, $\sim 3.0$ times solar, with clear evidence of a nuclear enhancement of N and He, possibly caused by massive star formation in the extended ($\sim 100$pc) central disk structure. The circum-nuclear narrow-line region spectrum is fit by a radiation pressure dominated photoionisation model model with an input EUV spectrum from a Black Hole with mass $5\times10^7 M_{\odot}$ radiating at $\sim 0.1$ of its Eddington luminosity. The bolometric luminosity is closely constrained to be $\log L_{\mathrm bol.} = 44.3\pm 0.1$ erg s$^{-1}$. The EUV spectrum characterised by a soft accretion disk and a harder component extending to above 15keV. The ENLR region is extended in the NW-SE direction. The line ratio variation in circum-nuclear spaxels can be understood as the result of mixing \ion{H}{ii} regions with an ENLR having a radius-invariant spectrum.

DELIVERY OF DUST GRAINS FROM COMET C/2013 A1 (SIDING SPRING) TO MARS

Comet C/2013 A1 (Siding Spring) will have a close encounter with Mars on October 19, 2014. We model the dynamical evolution of dust grains from the time of their ejection from the comet nucleus to the Mars close encounter, and determine the flux at Mars. Constraints on the ejection velocity from Hubble Space Telescope observations indicate that the bulk of the grains will likely miss Mars, although it is possible that a few-percent of grains with higher velocities will reach Mars, peaking approximately 90--100 minutes after the close approach of the nucleus, and consisting mostly of millimeter-radius grains ejected from the comet nucleus at a heliocentric distance of approximately 9~AU or larger. At higher velocities, younger grains from sub-millimeter to several millimeter can reach Mars too, although an even smaller fraction of grains is expected have these velocities, with negligible effect on the peak timing. Using NEOWISE observations of the comet, we can estimate that the maximum fluence will be of the order of $10^{-7}$ grains/m$^2$. We include a detailed analysis of how the expected fluence depends on the grain density, ejection velocity, and size-frequency distribution, to account for current model uncertainties and in preparation of possible refined model values in the near future.

AN EARLY LOOK OF COMET C/2013 A1 (SIDING SPRING): BREATHTAKER OR NIGHTMARE?

The dynamically new comet, C/2013 A1 (Siding Spring), is to make a close approach to Mars on 2014 October 19 at 18:30 UT at a distance of 40+/-1 Martian radius. Such extremely rare event offers a precious opportunity for the spacecrafts on Mars to closely study a dynamically new comet itself as well as the planet-comet interaction. Meanwhile, the high speed meteoroids released from C/Siding Spring also pose a threat to physically damage the spacecrafts. Here we present our observations and modeling results of C/Siding Spring to characterize the comet and assess the risk posed to the spacecrafts on Mars. We find that the optical tail of C/Siding Spring is dominated by larger particles at the time of the observation. Synchrone simulation suggests that the comet was already active in late 2012 when it was more than 7 AU from the Sun. By parameterizing the dust activity with a semi-analytic model, we find that the ejection speed of C/Siding Spring is comparable to comets such as the target of the Rosetta mission, 67P/Churyumov-Gerasimenko. Under nominal situation, the simulated dust cone will miss the planet by about 20 Martian radius. At the extreme ends of uncertainties, the simulated dust cone will engulf Mars, but the meteoric influx at Mars is still comparable to the nominal sporadic influx, seemly indicating that intense and enduring meteoroid bombardment due to C/Siding Spring is unlikely. Further simulation also suggests that gravitational disruption of the dust tail may be significant enough to be observable at Earth.

Perturbation of the Mars atmosphere by the near-collision with Comet C/2013 A1 (Siding Spring)

The martian upper atmosphere could be strongly perturbed by the near collision with Comet C/2013 A1 (Siding Spring). Significant mass and energy will be deposited in the upper atmosphere of Mars if the comet coma is sufficiently dense. We predict that comet H2O production rates larger than 1028 molecules/s would produce temperature increases exceeding 30K and the H density in the upper atmosphere will approximately double. The temperature perturbation will persist for several hours and the increased H density for tens of hours. Drag on orbiting spacecraft may increase by substantial factors, depending upon comet activity, because of the thermal perturbation to the atmosphere. Observation of these perturbations may provide insight into the thermal and chemical balances of the atmosphere.

Development and Experimental Validation of A Handheld Noninvasive Sensor for the Measurement of Compartment Pressures

Compartment syndrome is a major concern in cases of extremity trauma, which occur in over 70% of military combat casualty. Without treatment, compartment syndrome can lead to paralysis, loss of limb, or death. This paper focuses on the development of a handheld sensor that can be used for the noninvasive diagnosis of compartment syndrome. Analytical development of the sensing principle is first presented in which a relation is obtained between the pressure in a fluid compartment and the stiffness experienced by a handheld probe pushing on the compartment. Then a handheld sensor that can measure stiffness of an object without requiring the use of any inertial reference is presented. The handheld sensor consists of an array of three miniature force-sensing spring loaded pistons placed together on a probe. The center spring is chosen to be significantly stiffer than the side springs. The ratio of forces between the stiff and soft springs is proportional to the stiffness of the soft object against which the probe is pushed. Small millimeter-sized magnets on the pistons and magnetic field measurement chips are used to measure the forces in the individual pistons. Experimental results are presented using both an in vitro pneumatic test rig and a compliant agarose gel chamber that replicates a fluid pressure compartment. The sensor is shown to measure pressure accurately with a resolution of 0.1 psi over the range 0.75–2.5 psi. The developed sensor has the potential to be useful for convenient handheld diagnosis of compartment syndrome in traumatic extremity injuries.

The meteoroid fluence at Mars due to Comet C/2013 A1 (Siding Spring)

Long-period Comet C/2013 A1 (Siding Spring) will experience a close encounter with Mars on 2014 October 19. As of 2013 October 21, the distance of closest approach between the two is projected to be between 89,000km and 173,000km, with a nominal value of 131,000km. Thus, a collision between the comet and the planet has been ruled out, but the comet’s coma may very well envelop Mars and its man-made satellites. We present a simple analytic model of the dust component of cometary comae that describes the spatial distribution of cometary dust and meteoroids and their size distribution. We find that this model successfully reproduces, to within an order of magnitude, particle fluxes measured by spacecraft Giotto in the coma of 1P/Halley and by spacecraft Stardust in the coma of 81P/Wild 2. We apply our analytic model to C/2013 A1 (Siding Spring) and compute the expected total fluence of potentially damaging particles at Mars at the time of closest approach between the two bodies; we obtain a nominal fluence of 0.15 particles per square meter. We conduct numerical simulations of particle ejection from the comet’s nucleus and compare the resulting spatial distribution with that of our analytic model, and conclude that our spherically symmetric analytic model is adequate for order-of-magnitude fluence estimates.

Australian Astronomical Observatory

The Australian Astronomical Observatory (AAO) is a Division of the Australian Federal Government's Department of Innovation, Industry, Science, Research and Tertiary Education (DIISRTE). The AAO operates the Anglo-Australian Telescope (AAT) and the United Kingdom Schmidt Telescope (UKST) at Siding Spring Observatory, near Coonabarabran in north-western New South Wales. The AAO also hosts the Australian Gemini Office (AusGO) , which manages the allocation of time to Australian astronomers on the Gemini telescopes, as well as on Keck, Subaru and Magellan, through time-sharing or purchase agreements. The AAO's primary telescope facility, the AAT, is described here, with emphasis on its availability for international observers through our regular calls for proposals.

The effective temperature scale of M dwarfs

Despite their large number in the Galaxy, M dwarfs remain elusive objects and the modeling of their photospheres has long remained a challenge (molecular opacities, dust cloud formation). Our objectives are to validate the BT-Settl model atmospheres, update the M dwarf T eff -spectral type relation, and find the atmospheric parameters of the stars in our sample. We compare two samples of optical spectra covering the whole M dwarf sequence with the most recent BT-Settl synthetic spectra and use a \c{hi}2 minimization technique to determine Teff . The first sample consists of 97 low-resolution spectra obtained with NTT at La Silla Observatory. The second sample contains 55 mid-resolution spectra obtained at the Siding Spring Observatory (SSO). The spectral typing is realized by comparison with already classified M dwarfs. We show that the BT-Settl synthetic spectra reproduce the slope of the spectral energy distribution and most of its features. Only the CaOH band at 5570{\AA} and AlH and NaH hydrides in the blue part of the spectra are still missing in the models. The Teff-scale obtained with the higher resolved SSO 2.3 m spectra is consistent with that obtained with the NTT spectra. We compare our Teff scale with those of other authors and to published isochrones using the BT-Settl colors. We also present relations between effective temperature, spectral type and colors of the M dwarfs.

On-Sky Demonstration of a Fluid Atmospheric Dispersion Corrector

ABSTRACTThe first on-sky demonstration of a fluid atmospheric dispersion corrector (FADC) is presented using the Anglo-Australian Telescope at Siding Spring Observatory. The atmospheric dispersion correction was observed with a three-colour CCD camera at the telescope’s Cassegrain focus. The FADC contains a pair of immiscible fluids in a small glass container placed very close to the telescope focal plane. A pair of fluid prisms is formed and the apex of the two prisms varies with telescope zenith angle because of gravity. Three chemicals were identified and tested for this purpose. We experimentally measured the FADC dispersion properties versus zenith angle and it is shown that its dispersion follows the tan(Z) law. We have been able to observe 6 stars at different zenith angles and show that the FADC can correct atmospheric dispersion up to 1′′ at a zenith angle of 52° across the visible spectral range of 400–700 nm. It is demonstrated that an FADC can function as a passive atmospheric dispersion corrector without any moving parts. Our on-sky measurement results show excellent agreement with the optical ray-tracing model.

HATSouth: A Global Network of Fully Automated Identical Wide-Field Telescopes11The HATSouth hardware was acquired by NSF MRI NSF/AST-0723074 and is owned by Princeton University. The HATSouth network is operated by a collaboration consisting of Princeton University (PU), the Max Planck Institute for Astronomy (MPIA), and the Australian National University (ANU). The station at Las Campanas Observatory (LCO), of the Carnegie

ABSTRACTHATSouth is the world’s first network of automated and homogeneous telescopes that is capable of year-round 24 hr monitoring of positions over an entire hemisphere of the sky. The primary scientific goal of the network is to discover and characterize a large number of transiting extrasolar planets, reaching out to long periods and down to small planetary radii. HATSouth achieves this by monitoring extended areas on the sky, deriving high precision light curves for a large number of stars, searching for the signature of planetary transits, and confirming planetary candidates with larger telescopes. HATSouth employs six telescope units spread over three prime locations with large longitude separation in the southern hemisphere (Las Campanas Observatory, Chile; HESS site, Namibia; Siding Spring Observatory, Australia). Each of the HATSouth units holds four 0.18 m diameter f/2.8 focal ratio telescope tubes on a common mount producing an 8.2° × 8.2° field of view on the sky, imaged using four 4 K × 4 K CCD cameras and Sloan r filters, to give a pixel scale of 3.7″ pixel-1. The HATSouth network is capable of continuously monitoring 128 square arc degrees at celestial positions moderately close to the anti-solar direction. We present the technical details of the network, summarize operations, and present detailed weather statistics for the three sites. Robust operations have meant that on average each of the six HATSouth units has conducted observations on ∼500 nights over a 2 years time period, yielding a total of more than 1 million science frames at a 4 minute integration time and observing ∼10.65 hr day-1 on average. We describe the scheme of our data transfer and reduction from raw pixel images to trend-filtered light curves and transiting planet candidates. Photometric precision reaches ∼6 mmag at 4 minute cadence for the brightest non-saturated stars at r ≈ 10.5. We present detailed transit recovery simulations to determine the expected yield of transiting planets from HATSouth. We highlight the advantages of networked operations, namely, a threefold increase in the expected number of detected planets, as compared to all telescopes operating from the same site.

Characterisation of the Optical Turbulence at Siding Spring

AbstractMeasurements of the optical turbulence profile above Siding Spring Observatory were conducted during 2005 and 2006. This effort was largely motivated by the need to predict the statistical performance of adaptive optics at Siding Spring. The data were collected using a purpose-built instrument based on the slope detection and ranging (SLODAR) method where observations of a bright double star are imaged by Shack–Hartmann taken with the Australian National University 24-inch and 40-inch telescopes. The analysis of the data yielded a model consisting of a handful of statistically prominent thin layers that are statistically separated into the ground layer (37.5, 250 m) and the free atmosphere (1, 3, 6, 9, 13.5 km) for good (25%), typical (50%), and bad (25%) observing conditions. We found that ground-layer turbulence dominates the turbulence profile with up to 80% of the integrated turbulence below 500 m. The turbulence tends to be non-Kolmogorov, especially for the ground layer with a power-law index of β ~ 10/3. The mirror/dome seeing can be a significant fraction of the ground-layer turbulence. The median atmospheric seeing is around 1.2 arcsec, in agreement with observational reports.

Shaking Table Test of Vertical Isolation Device

In this paper, the performance verification study on a recently developed vertical vibration isolator is presented. The vertical seismic isolation system consists of four wedge-shape steel parts which provide friction surface at their interfaces, a center and two side springs, and a lateral bar which functions as a guide to side springs. The theoretical model for the isolator derived from the force equilibrium relationship is verified via numerical analyses and prototype tests. The performance of the isolator is further verified using the shaking table test. The analytical and experimental studies show that the isolator can reduce the vertical vibration effectively.

Adaptive Optics Simulations for Siding Spring

AbstractUsing an observationally derived model of optical turbulence profile, we have investigated the performance of adaptive optics (AO) at Siding Spring Observatory, Australia. The simulations cover the performance for AO techniques of single-conjugate adaptive optics (SCAO), multi-conjugate adaptive optics (MCAO), and ground-layer adaptive optics (GLAO). The simulation results presented in this paper predict the performance of these AO techniques as applied to the Australian National University (ANU) 2.3-m and Anglo-Australian Telescope (AAT) 3.9-m telescopes for astronomical wavelength bands J, H, and K. The results indicate that the AO performance is best for the longer wavelengths (K band) and in the best seeing conditions (sub 1 arcsec). The most promising results are found for GLAO simulations (field of view of 180 arcsec), with the field RMS for encircled energy 50% diameter (EE50d) being uniform and minimally affected by the free-atmosphere turbulence. The GLAO performance is reasonably good over the wavelength bands of J, H, and K. The GLAO field mean of EE50d is between 200 and 800 mas, which is a noticeable improvement compared with the nominal astronomical seeing (870–1 700 mas).

Testing Potential New Sites for Optical Telescopes in Australia

AbstractIn coming years, Australia may find the need to build new optical telescopes to continue local programmes, contribute to global survey projects, and form a local multi-wavelength connection for the new radio telescopes being built. In this study, we refine possible locations for a new optical telescope by studying remotely sensed meteorological infrared data to ascertain expected cloud coverage rates across Australia, and combine these data with a digital elevation model using a geographic information system. We find that the best sites within Australia for building optical telescopes are likely to be on the highest mountains in the Hamersley Range in northwest Western Australia, while the MacDonnell Ranges in the Northern Territory may also be appropriate. We believe that similar seeing values to Siding Spring should be obtainable and with significantly more observing time at the identified sites. We expect to find twice as many clear nights as at current telescope sites. These sites are thus prime locations for future on-site testing.

Surveillance, Surveillance, Surveillance

This presentation is a compilation of my three video installations, Your Universe – Inner Dome, Star Dome and Clear Clear Clear Target Star (2009). The collection of video-work shows the hidden and usually unseen aspects of astronomical exploration collected while at the Siding Spring Observatory in New South Wales, Australia. Each video is filmed directly from the monitor screens in the operations room that imaged the inner dome, the sky/star dome and the targeted star while the universe was being surveyed. The videos engender multi-levels of surveillance to become a comment on our need for such surveillance, to take control over what we do not understand, what is intangible and that which is unreachable.

Forbidden oxygen lines in Comets C/2006 W3 Christensen and C/2007 Q3 Siding Spring at large heliocentric distance: Implications for the sublimation of volatile ices

We present observations and analysis of the forbidden oxygen lines in Comets C/2006 W3 (Christensen) and C/2007 Q3 (Siding Spring) at heliocentric distances of 3.13 and 2.96AU, respectively. We obtained the observations using the ARCES echelle spectrometer, which is mounted on the Astrophysical Research Consortium 3.5-m telescope at Apache Point Observatory. We detected the 5577, 6300, and 6364Å atomic oxygen lines in Christensen and we calculated the ratio of the green (5577Å) line flux to that of the red doublet (6300 and 6364Å). We obtained a ratio of 0.24±0.08, a number higher than previous measurements for other comets at smaller heliocentric distance. This shows that CO and/or CO2 made detectable contributions to the O I population in the coma of Christensen. We only detected the 6300Å line in Siding Spring, resulting in an upper limit for the oxygen line ratio of 0.20. Based on the derived flux for the 6300Å line, we constrain the CO2 and H2O production rate in Siding Spring. A comparison of our results at ∼3AU to previous findings for comets at this approximate heliocentric distance suggests that a heliocentric distance of 3AU is a transition region between H2O and CO2 dominated activity in comets.

2008 LC18: a potentially unstable Neptune Trojan

The recent discovery of the first Neptune Trojan at the planet's trailing (L5) Lagrange point, 2008 LC18, offers an opportunity to confirm the formation mechanism of a member of this important tracer population for the Solar system's dynamical history. We tested the stability of 2008 LC18's orbit through a detailed dynamical study, using test particles spread across the orbital uncertainties in a, e, i and {\Omega}. This showed that the wide uncertainties of the published orbit span regions of both extreme dynamical instability, with lifetimes < 100 Myr, and with significant stability (> 1 Gyr lifetimes). The stability of 2008 LC18's clones is greatly dependent on their semi-major axis and only weakly correlated with their eccentricity. Test particles on orbits with an initial semi-major axis less than 29.91 AU have dynamical half-lives shorter than 100 Myr; in contrast, particles with an initial semi-major axis greater than 29.91 AU exhibit such strong dynamical stability that almost all are retained over the 1 Gyr of our simulations. More observations of this object are necessary to improve the orbit. If 2008 LC18 is in the unstable region, then our simulations imply that it is either a temporary Trojan capture, or a representative of a slowly decaying Trojan population (like its sibling the L4 Neptunian Trojan 2001 QR322), and that it may not be primordial. Alternatively, if the orbit falls into the larger, stable region, then 2008 LC18 is a primordial member of the highly stable and highly inclined component of the Neptune Trojan population, joining 2005 TN53 and 2007 VL305. We attempted to recover 2008 LC18 using the 2.3m telescope at Siding Spring Observatory to provide this astrometry, but were unsuccessful due to the high stellar density of its current sky location near the galactic centre. The recovery of this object will require a telescope in the 8m class.

The kinematical evolution of the Galactic disk

We present preliminary results from follow-up observations of a carefully selected sample of subgiant stars from RAVE and Geneva-Copenhagen surveys. We find evidence of rapid saturation of the heating mechanism in the disk, with an abrupt increase of the velocity dispersion for stars older than 9 Gyr. 1. SAMPLE DEFINITION AND FOLLOW-UP OBSERVATIONS Using high resolution spectroscopy data (7) showed the value of subgiants for dating the Galactic disk. We have selected ∼2000 subgiants candidates from the RAVE survey using RAVEs stellar parameters (6, 8). We have also selected 404 subgiants (no binaries) from the Geneva-Copenhagen survey (GCS) (3 )i n the Mv−Teff plane. We performed follow-up observations with the Double Beam Spectrograph (DBS) instrument mounted at the ANU 2.3 m telescope in Siding Spring Observatory. We use a long slit of 5 �� width and the 300B grating, giving a spectral resolution of R = /∼400. The recorded spectra cover the wavelength range from 3200 A to 6600 A. Observations consist of a sequence of target exposure, standard stars, calibration lamps, flats and bias. During the observational campaign we used a wide slit of 5 �� , which assures that 100% of the star light is collected (depending on the seeing), while avoid tracking problems. We also placed the slit parallel to the direction of atmosphere dispersion, i.e, aligning the slit at the parallactic angle to avoid recording incorrect intensities as a function of wavelength that could spoil our flux calibration. Standard stars with the same instrumental setup were obtained each night covering a large range of airmass over the night. This allows us to control the atmospheric extinction in the observed spectra. The final spectra present a typical S/N∼130 at 5500A and a S/N∼80 for the Ca II H & K region around 3950 A. A total of 1253 subgiant candidates spectra were obtained. 2. STELLAR PARAMETERS FROM SPECTROPHOTOMETRY We derived the stellar parameters using a chi-square minimization technique using empirical model atmospheres from the MILES library (4). The library consist of ∼1000 stars spanning a large range in atmospheric parameters. The spectra cover the range 3525-7500A at 2.3A (FWHM) spectral resolution. This technique allows us to derive accurate parameters from low resolution spectrophotometry via flux calibrated spectra. For reddening corrections we use the standard value of R(V) = A(V)/ E(B − V) = 3.1. We redden the model and we use the E(B − V) as a free parameter together with Teff , (M/H) and log g in the 2 fitting. Reddening effects are not large for our stars, as the selected RAVE stars are at |b |≥ 25 degrees and the GCS stars are in a very local volume with a radius lower than 100 pc.

THE SOLAR NEIGHBORHOOD. XXVI. AP Col: THE CLOSEST (8.4 pc) PRE-MAIN-SEQUENCE STAR

We present the results of a multi-technique investigation of the M4.5Ve flare star AP Col, which we discover to be the nearest pre-main-sequence star. These include astrometric data from the CTIO 0.9m, from which we derive a proper motion of 342.0+/-0.5 mas yr^-1, a trigonometric parallax of 119.21+/-0.98 mas (8.39+/-0.07 pc), and photometry and photometric variability at optical wavelengths. We also provide spectroscopic data, including radial velocity (22.4+/-0.3 km s^-1), lithium Equivalent Width (EW) (0.28+/-0.02 A), H-alpha EW (-6.0 to -35 A), {\it vsini} (11+/-1 km s^-1), and gravity indicators from the Siding Spring 2.3-m WiFeS, Lick 3-m Hamilton echelle, and Keck-I HIRES echelle spectrographs. The combined observations demonstrate that AP Col is the closer of only two known systems within 10 pc of the Sun younger than 100 Myr. Given its space motion and apparent age of 12-50 Myr, AP Col is likely a member of the recently proposed ~40 Myr old Argus/IC 2391 association.

SkyMapper Filter Set: Design and Fabrication of Large-Scale Optical Filters

ABSTRACTThe SkyMapper Southern Sky Survey will be conducted from Siding Spring Observatory with u, v, g, r, i, and z filters that comprise glued glass combination filters with dimensions of 309 × 309 × 15 mm. In this article we discuss the rationale for our bandpasses and physical characteristics of the filter set. The u, v, g, and z filters are entirely glass filters, which provide highly uniform bandpasses across the complete filter aperture. The i filter uses glass with a short-wave pass coating, and the r filter is a complete dielectric filter. We describe the process by which the filters were constructed, including the processes used to obtain uniform dielectric coatings and optimized narrowband antireflection coatings, as well as the technique of gluing the large glass pieces together after coating using UV transparent epoxy cement. The measured passbands, including extinction and CCD QE, are presented.