Cerro Pachon Research Articles

Mass Ratio of Single-line Spectroscopic Binaries with Visual Orbits Using Bayesian Inference and Suitable Priors* *Based in part on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovaçãoes (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at

We present orbital elements for 22 single-line binaries, nine of them studied for the first time, determined from a joint spectroscopic and astrometric solution. The astrometry is based on interferometric measurements obtained with the HRCam Speckle camera on the SOAR 4.1 m telescope at Cerro Pachon, Chile, supplemented with historical data. The spectroscopic observations were secured using Echelle spectrographs (FEROS, FIDEOS, and HARPS) at La Silla, Chile. A comparison of our orbital elements and systemic velocities with previous studies, including Gaia radial velocities, shows the robustness of our estimations. By adopting suitable priors of the trigonometric parallax and spectral type of the primary component, and using a Bayesian inference methodology developed by our group, we were able to estimate mass ratios for these binaries. Combining the present results with a previous study of other single-line binaries from our team, we present a pseudo mass-to-luminosity relationship based on 23 systems (46 stars) in the mass range 0.6 ≤ M ⊙ ≤ 2.5. We find a reasonable correspondence with a fiducial mass-to-luminosity relationship. We conclude that our methodology does allow us to derive tentative mass ratios for these types of binaries.

The Nature of Blue Stars with Mid-infrared Excesses in the Large Magellanic Cloud

We present low-resolution optical spectra and classifications of 92 blue objects with mid-infrared excesses in the Large Magellanic Cloud. The majority of these objects were selected with the criteria of U − B < 0 and V < 17 from the potential young stellar object (YSO) candidates in Gruendl & Chu (GC09), which were identified based on Spitzer Infrared Array Camera and Multiband Imaging Photometer for Spitzer observations in conjunction with optical photometry from the Magellanic Clouds Photometric Survey. Many of the sample objects have ambiguous classifications. We examined the properties of these 92 objects using low-resolution optical spectra obtained with the SOAR 4.1 m Telescope at Cerro Pachon and the Blanco 4 m Telescope at Cerro Tololo Inter-American Observatory, supplemented by available photometric and imaging observations. We estimated the spectral types, temperatures, and luminosities of these objects from the optical to near-IR spectral energy distributions based on the photometric data, and further examined stellar absorption line features in the optical spectra to verify the spectral types. The interstellar/circumstellar environments, assessed from nebular line imaging observations and nebular lines detected in the stellar spectra, further helped constrain the nature of stars. Among these 92 objects, we confirm 42 stars as YSOs, and the remaining 50 objects as protoplanetary nebulae, post-AGB/RGB stars, blue evolved massive stars, stars with dust in vicinity, or uncertain classifications. Our results show that the photometric criteria in GC09 are generally effective in the initial selection of YSO candidates, and the low-resolution spectroscopy combined with environment assessment can be useful to better constrain the classifications and ameliorate most ambiguities.

Mesosphere and Lower Thermosphere Changes Associated With the 2 July 2019 Total Eclipse in South America Over the Andes Lidar Observatory, Cerro Pachon, Chile

AbstractThis article presents the results of a week of observations around the 2 July 2019, total Chilean eclipse. The eclipse occurred between 19:22 and 21:46 UTC, with complete sun disc obscuration at 20:38–20:40 UTC (16:38–16:40 LT) over the Andes Lidar Observatory (ALO) at (30.3°S, 70.7°W). Observations were carried out using ALO instrumentation with the goal to observe possible eclipse‐induced effects on the mesosphere and lower thermosphere region (MLT; 75–105 km altitude). To complement our data set, we have also utilized TIMED/SABER temperatures and ionosonde electron density measurements taken at the University of La Serena's Juan Soldado Observatory. Observed events include an unusual fast, bow‐shaped gravity wave structure in airglow images, mesosphere temperature mapper brightness as well as in lidar temperature with 150 km horizontal wavelength 24 min observed period, and vertical wavelength of 25 km. Also, a strong zonal wind shear above 100 km in meteor radar scans as well as the occurrence of a sporadic E layer around 100 km from ionosonde measurements. Finally, variations in temperature and density and the presence of a descending sporadic sodium layer near 98 km were seen in lidar data. We discuss the effects of the eclipse in the MLT, which can shed light on a sparse set of measurements during this type of event. Our results point out several effects of eclipse‐associated changes in the atmosphere below and above but not directly within the MLT.

Optimal Prediction of Atmospheric Turbulence by Means of the Weather Research and Forecasting Model

The performance of ground-based astronomical observations and free-space optical communication (FSOC) systems suffers from atmospheric turbulence and meteorological conditions. The a priori knowledge of atmospheric conditions several hours before observations allows the programming of astronomical observations (flexible scheduling) to be optimized. In this paper, we present a prediction study based on the Weather Research and Forecasting (WRF) model. It allows the prediction and characterization of a useful set of meteorological parameters relevant to atmospheric physics (e.g., pressure, temperature, relative humidity, wind speed, and direction). Predicted parameters are then injected into an optical turbulence (OT) model to compute the refractive index structure constant C n 2. We performed sets of simulations for Cerro Pachon Observatory in Chile, using the data from the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR). The main goal is to quantify how accurately numerical weather prediction models can reproduce conditions over the complex terrain of the Cerro Pachon area. In order to produce a reliable forecast, meteorological prognostic skills need accurate representations of the physical parameterization options. Three widely used Planetary Boundary Layer (PBL) schemes and two Land Surface Models (LSM) were tested, analyzed, and compared in order to find the optimal WRF configuration. Predictions are compared to in situ measurements coming from balloon-borne radiosoundings. It is determined that the predicted C n 2 are in good agreement with the radiosoundings measurements with a mean relative error (MRE) under 6.4% at all altitudes when using balloon measurements to deduce some parameters such as the outer scale of turbulence L 0, which is used in the OT model. For a fully operational prediction, the MREs between the predictions and the measurements range from 1.4% to 8% according to the different ways to estimate the L 0 profiles. Seasonal statistics are also presented for different meteorological and turbulence parameters.

Statistical Spectral Characteristics of Three‐Dimensional Winds in the Mesopause Region Revealed by the Andes Lidar

AbstractBy analyzing data recorded at the Andes Lidar Observatory in Cerro Pachon, Chile (30.3°S, 70.7°W) from May 2014 to July 2019, we investigated the fundamental features of three‐dimensional wind and temperature spectra. The vertical wavenumber spectral amplitudes of horizontal winds show obvious seasonal variations that are closely related to the seasonal variations in the source and background winds. The wavenumber spectral slopes of the horizontal winds are systematically less negative than −3, with mean values of −1.96 and −2.18 for zonal and meridional winds, respectively. The zonal and meridional wind frequency spectra have mean slopes of −1.37 and −1.56, respectively; these values are slightly less negative than −5/3. Moreover, the frequency spectral amplitudes show different seasonal variations from those of the wavenumber spectra, possibly because they correspond to different GW spectral components. The vertical wind has obviously different spectral features than the horizontal winds. The vertical wind spectra are notably shallower than the horizontal wind spectra, with mean slopes of −0.82 and −0.91 for the wavenumber and frequency spectra, respectively, departing evidently from those expected under linear instability theory (LIT). Although the vertical wind spectrum is almost always separable, the horizontal wind spectra are separable only at high frequencies. As the frequency increased, the horizontal wind wavenumber spectra become shallower and depart from the spectral slope expected under LIT, likely because high‐frequency GWs are not completely saturated. In general, our results do not support LIT.

Impact of Rubin Observatory LSST Template Acquisition Strategies on Early Science from the Transients and Variable Stars Science Collaboration: Non-time-critical Science Cases

Vera C. Rubin Observatory Legacy Survey of Space and Time, LSST, will revolutionize modern astronomy by producing an extremely deep (coadded depth ~27 mag) depth-limited survey of the entire southern sky (LSST Science Collaboration et al. 2009). The 8.4 m large-aperture, wide-field telescope, which is based in Cerro Pachon, will image the entire Southern sky every three nights in multiple bands (SDSS-u, g, r, i, z, y) and produce a fire-hose of data, 20 Tb each night, concluding in a 60 petabyte data set as the legacy of the 10 yr survey. Extracting meaningful light curves from variable objects requires difference imaging to both identify variability and calibrate light curve data products. Templates, co-added groups of visits that act as an image of the static sky, are a key component of Difference Imaging Analysis (DIA) and as such are of paramount importance for all science that involves variable objects. As the non-time-critical science cases discussed here are mostly periodic, they generally do not depend upon the survey alert stream; however, templates are still crucial for performing science and calibrations during the first year. We provide recommendations for observing strategies for template acquisition starting from commissioning and through Year 1 of the survey.

Observations of the Breakdown of Mountain Waves Over the Andes Lidar Observatory at Cerro Pachon on 8/9 July 2012

AbstractAlthough mountain waves (MWs) are thought to be a ubiquitous feature of the wintertime southern Andes stratosphere, it was not known whether these waves propagated up to the mesopause region until Smith et al. (2009) confirmed their presence via airglow observations. The new Andes Lidar Observatory at Cerro Pachon in Chile provided the opportunity for a further study of these waves. Since MWs have near‐zero phase speed, and zero wind lines often occur in the winter upper mesosphere (80 to 100 km altitude) region due to the reversal of the zonal mean and tidal wind, MW breakdown may routinely occur at these altitudes. Here we report on very high spatial/temporal resolution observations of the initiation of MW breakdown in the mesopause region. Because the waves are nearly stationary, the breakdown process was observed over several hours; a much longer interval than has previously been observed for any gravity wave breakdown. During the breakdown process observations were made of initial horseshoe‐shaped vortices, leading to successive vortex rings, as is also commonly seen in Direct Numerical Simulations (DNS) of idealized and multiscale gravity wave breaking. Kelvin‐Helmholtz instability (KHI) structures were also observed to form. Comparing the structure of observed KHI with the results of existing DNS allowed an estimate of the turbulent kinematic viscosity. This viscosity was found to be around 25 m2/s, a value larger than the nominal viscosity that is used in models.

LSST and the Epoch of Reionization Experiments

AbstractThe Large Synoptic Survey Telescope (LSST), a next generation astronomical survey, sited on Cerro Pachon in Chile, will provide an unprecedented amount of imaging data for studies of the faint optical sky. The LSST system includes an 8.4m (6.7m effective) primary mirror and a 3.2 Gigapixel camera with a 9.6 sq. deg. field of view. This system will enable about 10,000 sq. deg. of sky to be covered twice per night, every three to four nights on average, with typical 5-sigma depth for point sources ofr= 24.5 (AB). With over 800 observations in theugrizybands over a 10-year period, these data will enable coadded images reachingr= 27.5 (about 5 magnitudes deeper than SDSS) as well as studies of faint time-domain astronomy. The measured properties of newly discovered and known astrometric and photometric transients will be publicly reported within 60 sec after closing the shutter. The resulting hundreds of petabytes of imaging data for about 40 billion objects will be used for scientific investigations ranging from the properties of near-Earth asteroids to characterizations of dark matter and dark energy. For example, simulations estimate that LSST will discover about 1,000 quasars at redshifts exceeding 7; this sample will place tight constraints on the cosmic environment at the end of the reionization epoch. In addition to a brief introduction to LSST, I review the value of LSST data in support of epoch of reionization experiments and discuss how international participants can join LSST.

Ethics and the Social Impact of Computational Intelligence [President's Message

At the time of writing this column, I have just finished a tour in Chile & Argentina with the Executive Committee (EXCOM) of the IEEE Computational Intelligence Society (CIS). As part of our geographical outreach program we organized CIS workshops at La Serena University, in northern Chile; the University of Chile, in Santiago; and the University of Buenos Aires, in Argentina. In Chile we had the opportunity to visit the astronomy observatories located near La Serena. Dr. Chris Smith, an astronomer and the head of mission, AURA Observatory in Chile, was our knowledgeable host. The actual telescope sites are located in an area of more than 90,000 acres that includes two operational mountaintops, Cerro Tololo at 2,200 m, and Cerro Pachon at 2,750 m. Tololo is a very famous place, because the discovery of the accelerated expansion of the Universe was made in these facilities. Pachon is the place where the new generation telescope named LSST is being built.

Everything we’d like to do with LSST data, but we don’t know (yet) how

AbstractThe Large Synoptic Survey Telescope (LSST), the next-generation optical imaging survey sited at Cerro Pachon in Chile, will provide an unprecedented database of astronomical measurements. The LSST design, with an 8.4m (6.7m effective) primary mirror, a 9.6 sq. deg. field of view, and a 3.2 Gigapixel camera, will allow about 10,000 sq. deg. of sky to be covered twice per night, every three to four nights on average, with typical 5-sigma depth for point sources of r=24.5 (AB). With over 800 observations in ugrizy bands over a 10-year period, these data will enable a deep stack reaching r=27.5 (about 5 magnitudes deeper than SDSS) and faint time-domain astronomy. The measured properties of newly discovered and known astrometric and photometric transients will be publicly reported within 60 sec after observation. The vast database of about 30 trillion observations of 40 billion objects will be mined for the unexpected and used for precision experiments in astrophysics. In addition to a brief introduction to LSST, we discuss a number of astro-statistical challenges that need to be overcome to extract maximum information and science results from LSST dataset.

LSST survey: millions and millions of quasars

AbstractThe Large Synoptic Survey Telescope (LSST), the next-generation optical imaging survey sited at Cerro Pachon in Chile, will provide hundreds of detections for a sample of more than ten million quasars with redshifts up to about seven. The LSST design, with an 8.4m (6.7m effective) primary mirror, a 9.6 sq. deg. field of view, and a 3.2 Gigapixel camera, will allow about 10,000 sq. deg. of sky to be covered twice per night, every three to four nights on average, with typical 5-sigma depth for point sources of r=24.5 (AB). With about 1000 observations in ugrizy bands over a 10-year period, these data will enable a deep stack reaching r=27.5 (about 5 magnitudes deeper than SDSS) and faint time-domain astronomy. The measured properties of newly discovered and known astrometric and photometric transients will be publicly reported within 60 sec after closing the shutter. In addition to a brief introduction to LSST, I review optical quasar selection techniques, with emphasis on methods based on colors, variability properties, and astrometric behavior.

A daytime measurement of the lunar contribution to the night sky brightness in LSST’s ugrizy bands–initial results

We report measurements from which we determine the spatial structure of the lunar contribution to night sky brightness, taken at the LSST site on Cerro Pachon in Chile. We use an array of six photodiodes with filters that approximate the Large Synoptic Survey Telescope's {\it u, g, r, i, z,} and {\it y} bands. We use the sun as a proxy for the moon, and measure sky brightness as a function of zenith angle of the point on sky, zenith angle of the sun, and angular distance between the sun and the point on sky. We make a correction for the difference between the illumination spectrum of the sun and the moon. Since scattered sunlight totally dominates the daytime sky brightness, this technique allows us to cleanly determine the contribution to the (cloudless) night sky from backscattered moonlight, without contamination from other sources of night sky brightness. We estimate our uncertainty in the relative lunar night sky brightness vs. zenith and lunar angle to be 10\,\%. This information is useful in planning the optimal execution of the LSST survey, and perhaps for other astronomical observations as well. Although our primary objective is to map out the angular structure and spectrum of the scattered light from the atmosphere and particulates, we also make an estimate of the expected number of scattered lunar photons per pixel per second in LSST, and find values that are in overall agreement with previous estimates.

Site Protection Efforts at the AURA Observatory in Chile

AbstractThe AURA Observatory site in northern Chile, which includes Cerro Tololo and Cerro Pachon, has been operational for over 50 years now, facing a variety of challenges to its long-term future. The site now hosts over 20 operational telescopes, ranging from small projects with 0.4m telescopes to the Blanco 4m, the SOAR 4.1m, and the 8m Gemini-South telescopes. In addition, we have recently begun the construction of the Large Synoptic Survey Telescope (LSST) on the summit of Cerro Pachon. We summarize our efforts over the past 20-30 years to highlight the importance of site protection through education and public outreach as well as through more recent promotion of IDA certifications in the region and support for the World Heritage initiatives described by others in this conference.

TRIENNIAL REPORT

This triennium has seen progress in a number of directions related to Commission 20 objectives. Foremost, the growth in the number of astrometric observations of small solar system bodies continues to accelerate and the total number of measurements recorded by the Minor Planet Center now exceeds 135 million. Currently the Pan-STARRS project and the Catalina Sky Survey (CSS) dominate detection and discovery efforts, while the NEO-WISE space mission contributes infrared detections valuable for understanding the size distribution of populations. Looking forward, the Large Synoptic Survey Telescope (LSST) is now funded and in construction on Cerro Pachon in Chile. LSST has the potential to revolutionize the field by conducting a multi-color, ten-year, all-sky survey with a limiting magnitude ~24.5 in the r-band. Survey operations are set to begin in 2022.

Simultaneous observations of the phase‐locked 2 day wave at Adelaide, Cerro Pachon, and Darwin

AbstractThe Southern Hemisphere summer 2 day wave (TDW) is the most dramatic large‐scale event of the upper mesosphere. The winds accelerate over ~1 week, may attain &gt; 70 m/s, and are often accompanied by a near disappearance of the diurnal tide and stabilization of the period close to 48 h. We denote this as the phase‐locked 2 day wave (PL/TDW). We have examined airglow and meteor radar (MR) wind data from the Andes Lidar Observatory (Cerro Pachon, Chile:30°S, 289.3°E), MR data from Darwin (12.5°S, 131°E) and airglow and medium frequency radar data from the University of Adelaide (34.7°S, 138.6°E) for the behavior of the TDW during the austral summers of 2010, 2012, and 2013. The Cerro Pachon and Adelaide sites are located at similar latitudes separated in longitude by about 120°. We find a remarkable coincidence between the TDW oscillations at Chile and Adelaide for the period January–February 2010. The oscillations are nearly in phase in terms of local time and the minima and maxima repeat at nearly the same local time from cycle to cycle consistent with a phase‐locked wave number 3 TDW. Data for this and other years (including Darwin) show that the amplitude of the diurnal tide decreases when the TDW is largest and that this occurs when the period is close to 48 h. These observations support the proposal that the PL/TDW is a subharmonic parametric instability wherein the diurnal tide transfers energy to a TDW that is resonant at nearly 48 h.

The life cycle of instability features measured from the Andes Lidar Observatory over Cerro Pachon on 24 March 2012

AbstractThe Aerospace Corporation's Nightglow Imager (ANI) observes nighttime OH emission (near 1.6 μm) every 2 s over an approximate 73° field of view. ANI had previously been used to study instability features seen over Maui. Here we describe observations of instabilities seen from 5 to 8 UT on 24 March 2012 over Cerro Pachon, Chile, and compare them with previous results from Maui, with theory, and with Direct Numerical Simulations (DNS). The atmosphere had reduced stability because of the large negative temperature gradients measured by a Na lidar. Thus, regions of dynamical and convective instabilities are expected to form, depending on the value of the Richardson number. Bright primary instabilities are formed with a horizontal wavelength near 9 km and showed the subsequent formation of secondary instabilities, rarely seen over Maui, consistent with the primaries being dynamical instabilities. The ratio of the primary to secondary horizontal wavelength was greater over Chile than over Maui. After dissipation of the instabilities, smaller‐scale features appeared with sizes in the buoyancy subrange between 1.5 and 6 km. Their size spectra were consistent with the model of Weinstock (1978) if the turbulence is considered to be increasing. The DNS results produce secondary instabilities with sizes comparable to what is seen in the images although their spectra are somewhat steeper than is observed. However, the DNS results also show that after the complete decay of the primary features, scale sizes considerably smaller than 1 km are produced and these cannot be seen by the ANI instrument.

THE NUCLEUS OF MAIN-BELT COMET 259P/GARRADD

We present observations of the main-belt comet 259P/Garradd, previously known as P/2008 R1 (Garradd), obtained in 2011 and 2012 using the Gemini North Telescope on Mauna Kea in Hawaii, and the SOAR Telescope at Cerro Pachon in Chile, with the goal of computing the object's phase function and nucleus size. We find an absolute magnitude of $H_R=19.71\pm0.05$ mag and slope parameter of $G_R=-0.08\pm0.05$ for the inactive nucleus, corresponding to an effective nucleus radius of $r_e=0.30\pm0.02$ km, assuming an $R$-band albedo of $p_R=0.05$. We also revisit observations reported for 259P while it was active in 2008 to quantify the dust mass loss and compare the object with other known main-belt comets.

Temporal characterization of atmospheric turbulence with the Generalized Seeing Monitor instrument

The temporal behavior of atmospheric turbulence has been analyzed by means of angle-of-arrival (AA) fluctuation measurements. The temporal evolution of the main atmospheric optical parameters (AOP) have been studied in order to determine their stability. This is of interest because these AOP are necessary for the optimization of high angular resolution techniques. A new method of coherence time τ0 monitoring with the Generalized Seeing Monitor (GSM) is presented and the measurements obtained at major sites over the world are presented (La Silla, Cerro Pachon, Paranal, San Pedro Mártir, Mt Palomar, Mauna Kea, La Palma, Oukaïmeden, Maydanak).

TRANSIT MONITORING IN THE SOUTH (TraMoS) PROJECT: DISCARDING TRANSIT TIMING VARIATIONS IN WASP-5b

We report nine new transit epochs of the extrasolar planet, observed in the Bessell-I band with SOAR at the Cerro Pachon Observatory and with the SMARTS 1-m Telescope at CTIO, between August 2008 and October 2009. The new transits have been combined with all previously published transit data for this planet to provide a new Transit Timing Variations (TTVs) analysis of its orbit. We find no evidence of TTVs RMS variations larger than 1 min over a 3 year time span. This result discards the presence of planets more massive than about 5 M_earth, 1 M_earth and 2 M_earth around the 1:2, 5:3 and 2:1 orbital resonances. These new detection limits exceed by ~5-30 times the limits imposed by current radial velocity observations in the Mean Motion Resonances of this system. Our search for the variation of other parameters, such as orbital inclination and transit depth also yields negative results over the total time span of the transit observations. This result supports formation theories that predict a paucity of planetary companions to Hot Jupiters.

DISCOVERY AND CHARACTERIZATION OF AN EXTREMELY DEEP-ECLIPSING CATACLYSMIC VARIABLE: LSQ172554.8-643839

We report the discovery of an eclipsing cataclysmic variable with eclipse depths > 5.7 mag, orbital period 94.657 min, and peak brightness V~18 at J2000 position 17h 25m 54s.8, -64d 38' 39". Detected by visual inspection of images from Yale University's QUEST camera on the ESO 1.0-m Schmidt telescope at La Silla, we obtained light curves in B, V, R, I, z and J with the SMARTS 1.3-m and 1.0-m telescopes at Cerro Tololo and spectra from 3500 to 9000 Angstrom with the SOAR 4.3-m telescope at Cerro Pachon. The optical light curves show a deep, 5-min eclipse immediately followed by a shallow 38-min eclipse and then sinusoidal variation. No eclipses appear in J. During the deep eclipse we measure V-J > 7.1, corresponding to a spectral type M8 or later secondary, consistent with the dynamical constraints. The estimated distance is 150 psec. The spectra show strong Hydrogen emission lines, Doppler broadened by 600 - 1300 km/s, oscillating with radial velocity that peaks at mid deep eclipse with semi-amplitude 500 +/- 22 km/s. We suggest that LSQ172554.8-643839 is a polar with a low-mass secondary viewed at high inclination. No known radio or x-ray source coincides with the new object's location.