Shane Telescope Research Articles

Analysis of on-sky sodium profile data from Lick Observatory

The next generation of adaptive optics will depend on laser guide stars to increase sky coverage. However, there are a few limitations. The thickness of the sodium layer in the mesosphere at 90 km causes spot elongation, which is more severe for large telescopes. Moreover, the outer-edge subaperture of such large telescopes will resolve variations of sodium atom density seen over the thick layer. We quantify these density fluctuations using real data taken at Lick Observatory. We used the 1 m Nickel telescope to image the return flux due to laser-induced fluorescence from a dye laser launched from the nearby 3 m Shane telescope. This view was from the side allowing the resolution of the sodium return as a function of height. We used drift scanning of the 1 m telescope to provide resolution in time. We show qualitative images of the sodium distribution for different nights and quantitatively study the temporal power spectra of those fluctuations. We conclude that the sodium profiles have an average full width half-maximum of 10 km. However, the extent beyond the nominal 10 km thickness is important for accurate wavefront sensing. The variations in the height of the sodium layer occur on short enough time scales that AO systems for 30 m class telescopes will likely need focus updates on time scales shorter than 100 ms.

THE LICK AGN MONITORING PROJECT: BROAD-LINE REGION RADII AND BLACK HOLE MASSES FROM REVERBERATION MAPPING OF Hβ

We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~10^6-10^7 M_sun and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad Hbeta emission. We present here the light curves for the objects in this sample and the subsequent Hbeta time lags for the nine objects where these measurements were possible. The Hbeta lag time is directly related to the size of the broad-line region, and by combining the lag time with the measured width of the Hbeta emission line in the variable part of the spectrum, we determine the virial mass of the central supermassive black hole in these nine AGNs. The absolute calibration of the black hole masses is based on the normalization derived by Onken et al. We also examine the time lag response as a function of velocity across the Hbeta line profile for six of the AGNs. The analysis of four leads to ambiguous results with relatively flat time lags as a function of velocity. However, SBS 1116+583A exhibits a symmetric time lag response around the line center reminiscent of simple models for circularly orbiting broad-line region (BLR) clouds, and Arp 151 shows an asymmetric profile that is most easily explained by a simple gravitational infall model. Further investigation will be necessary to fully understand the constraints placed on physical models of the BLR by the velocity-resolved response in these objects.

An Improved Technique for the Photometry and Astrometry of Faint Companions

ABSTRACTWe propose a new approach to differential astrometry and photometry of faint companions in adaptive optics images. It is based on a prewhitening matched filter, also referred to in the literature as the Hotelling observer. We focus on cases where the signal of the companion is located within the bright halo of the parent star. Using real adaptive optics data from the 3 m Shane telescope at the Lick Observatory, we compare the performance of the Hotelling algorithm with other estimation algorithms currently used for the same problem. The real single-star data are used to generate artificial binary objects with a range of magnitude ratios. In most cases, the Hotelling observer gives significantly lower astrometric and photometric errors. In the case of high Strehl ratio (SR) data (SR ≈ 0.5), the differential photometry of a binary star with a Δm = 4.5 and a separation of 0.6″ is better than 0.1 mag; a factor of 2 lower than the other algorithms considered.

REFERENCE-LESS DETECTION, ASTROMETRY, AND PHOTOMETRY OF FAINT COMPANIONS WITH ADAPTIVE OPTICS

We propose a complete framework for the detection, astrometry, and photometry of faint companions from a sequence of adaptive optics corrected short exposures. The algorithms exploit the difference in statistics between the on-axis and off-axis intensity. Using moderate-Strehl ratio data obtained with the natural guide star adaptive optics system on the Lick Observatory's 3-m Shane Telescope, we compare these methods to the standard approach of PSF fitting. We give detection limits for the Lick system, as well as a first guide to expected accuracy of differential photometry and astrometry with the new techniques. The proposed approach to detection offers a new way of determining dynamic range, while the new algorithms for differential photometry and astrometry yield accurate results for very faint and close-in companions where PSF fitting fails. All three proposed algorithms are self-calibrating, i.e. they do not require observation of a calibration star thus improving the observing efficiency.

DEEP MIXING AND METALLICITY: CARBON DEPLETION IN GLOBULAR CLUSTER GIANTS

We present the results of an observational study of the efficiency of deep mixing in globular cluster red giants as a function of stellar metallicity. We determine [C/Fe] abundances based on low-resolution spectra taken with the Kast spectrograph on the 3m Shane telescope at Lick Observatory. Spectra centered on the 4300 Angstrom CH absorption band were taken for 42 bright red giants in 11 Galactic globular clusters ranging in metallicity from M92 ([Fe/H]=-2.29) to NGC 6712 ([Fe/H]=-1.01). Carbon abundances were derived by comparing values of the CH bandstrength index S2(CH) measured from the data with values measured from a large grid of SSG synthetic spectra. Present-day abundances are combined with theoretical calculations of the time since the onset of mixing, which is also a function of stellar metallicity, to calculate the carbon depletion rate across our metallicity range. We find that the carbon depletion rate is twice as high at a metallicity of [Fe/H]=-2.3 than at [Fe/H]=-1.3, which is a result qualitatively predicted by some theoretical explanations of the deep mixing process.

First Results from the Lick AGN Monitoring Project: The Mass of the Black Hole in Arp 151

We have recently completed a 64 night spectroscopic monitoring campaign at the Lick Observatory 3 m Shane telescope with the aim of measuring the masses of the black holes in 13 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~106-107 M☉. We present here the first results from this project—the mass of the central black hole in Arp 151. Strong variability throughout the campaign led to an exceptionally clean Hβ lag measurement in this object of 4.25−0.66+0.68 days in the observed frame. Coupled with the width of the Hβ emission line in the variable spectrum, we determine a black hole mass of (7.1 ± 1.2) × 106 M☉, assuming the Onken et al. normalization for reverberation-based virial masses. We also find velocity-resolved lag information within the Hβ emission line which clearly shows infalling gas in the Hβ-emitting region. Further detailed analysis may lead to a full model of the geometry and kinematics of broad line region gas around the central black hole in Arp 151.

Triaxial ellipsoid dimensions and rotational poles of seven asteroids from Lick Observatory adaptive optics images, and of Ceres

Seven main belt asteroids, 2 Pallas, 3 Juno, 4 Vesta, 16 Psyche, 87 Sylvia, 324 Bamberga, and 707 Interamnia, were imaged with the adaptive optics system on the 3 m Shane telescope at Lick Observatory in the near infrared, and their triaxial ellipsoid dimensions and rotational poles have been determined with parametric blind deconvolution. In addition, the dimensions and pole for 1 Ceres are derived from resolved images at multiple epochs, even though it is an oblate spheroid.

A Survey of 3.3 μm PAH Emission in Planetary Nebulae

Results are presented from a pilot survey of 3.3 μm PAH emission from planetary nebulae using FLITECAM, an instrument intended for airborne astronomy with SOFIA. The observations were made during ground-based commissioning of FLITECAM's spectroscopic mode at the 3 m Shane Telescope at Lick Observatory. Direct-ruled KRS-5 grisms were used to give a resolving power (R) ~ 1700. Targets were selected from IRAS, KAO, and ISO sources with previously observed PAH emission at longer wavelengths. AGB stars and PNe with C/O ratios <1 were also added to the target list in order to test PAH detection thresholds. In all, 20 objects were observed. PAH emission was detected in 11 out of 20 observed targets.

The Unusual Spectrum of Comet 96P/Machholz

We report spectra from 3000 to 5900 Å for comet 96P/Machholz, obtained on 2007 April 27 UT with the 3 m Shane telescope at Lick Observatory. The spectra are extremely carbon-poor, and they show a prominent NH2 series but no CN emission. NH, NH2, and C2 gas production rates are (8.36 ± 2.18) × 1025, (29.88 ± 3.66) × 1025, and (4.52 ± 0.61) × 1023 molecules s-1, respectively, as determined from Haser model fits to the data. Upper limits to the gas production rates for CN and C3 are 7.5 × 1022 and 2.0 × 1023, respectively. Although 96P is depleted in C2 and C3 relative to NH, it is even more depleted in CN than other so-called carbon chain-depleted comets.

Variability of Moderate‐Luminosity Active Galactic Nuclei atz= 0.36

We monitored 13 moderate-luminosity active galactic nuclei at z = 0.36 to measure flux variability, explore feasibility of reverberation mapping, and determine uncertainties on estimating black hole mass from single-epoch data. Spectra and images were obtained with approximately weekly cadence for up to 4 months, using the Kast spectrograph on the 3 m Shane Telescope. In broad band we detect peak-to-peak variations of 9%-37% and rms variations of 2%-10%. The observed flux variability in the g' band (rest frame 2800-4000 Å) is consistent with that in the r' band (rest frame 4000-5200 Å), but with larger amplitude. However, after correcting for stellar light dilution using Hubble Space Telescope images, we find nuclear variability of 3%-24% (rms variation) with similar amplitudes in the g' and r' bands within the errors. Intrinsic flux variability of the Hβ line is also detected at the 3%-13% level, after accounting for systematic errors on the spectrophotometry. This demonstrates that a reverberation mapping campaign beyond the local universe can be carried out with a 3 m class telescope, provided that sufficiently long light curves are obtained. Finally, we compare the Hβ FWHM measured from mean spectra with that measured from single-epoch data, and find no bias but an rms scatter of 14%, mostly accounted for by the uncertainty on FWHM measurements. The propagated uncertainty on black hole mass estimates, due to the FWHM measurement errors using low S/N (10-15 pixel-1) single-epoch spectra, is 30%.

Characterizing the Adaptive Optics Off‐Axis Point‐Spread Function. II. Methods for Use in Laser Guide Star Observations11Based on observations obtained at the Lick Observatory, which is operated by the University of California.

ABSTRACTMost current astronomical adaptive optics (AO) systems rely on the availability of a bright star to measure the distortion of the incoming wave front. Replacing the guide star with an artificial laser beacon alleviates this dependency on bright stars and therefore increases sky coverage, but it does not eliminate another serious problem for AO observations. This is the issue of PSF variation with time and field position near the guide star. In fact, because a natural guide star is still necessary for correction of the low‐order phase error, characterization of laser guide star (LGS) AO PSF spatial variation is more complicated than for a natural guide star alone. We discuss six methods for characterizing LGS AO PSF variation that can potentially improve the determination of the PSF away from the laser spot; that is, off‐axis. Calibration images of dense star fields are used to determine the change in PSF variation with field position. This is augmented by AO system telemetry and simple computer simulations to determine a more accurate off‐axis PSF. We report on tests of the methods using the laser AO system on the Lick Observatory Shane Telescope. We observed with offsets typical of separations between dim science targets and the nearest suitably bright tip‐tilt guide star, up to 20″. If the tip‐tilt guide star is used as the PSF reference, the predicted Strehl ratio within an 8″ radius of the LGS can be more than a factor of 2 too high, as it does not take into account the field‐dependent anisoplanatism. A better result may be obtained by an improved empirical approach: repositioning the tip‐tilt guide star to compensate for the additional 8″ offset. This would result in a 27% relative error in Strehl ratio. A simple Gaussian model of PSF variation can reduce the error in the prediction to ∼20%. Some further improvement may be obtained semianalytically by using telemetry from the AO system (14% error) plus a more sophisticated theoretical model of PSF variation (13% error). It should be noted, however, that all but the first method achieve comparable accuracy in predicting PSF FWHM. This is important because the last method, unlike the others, is not directly applicable to 10 m apertures without further computational complexity.

The Kast Ground-based Ultraviolet Spectral Survey of 79 Quasi-stellar Objects at Redshift 2 for Lyα Forest and Metal Absorption

We present spectra of 79 bright QSOs obtained with the Kast spectrograph on the 3 m Shane Telescope at Lick Observatory. The QSOs have emission redshifts 1.89–2.45, and most are near the mean value of zem = 2.17. Two of them, one a new discovery, are broad absorption line QSOs. The spectra have ~250 km s-1 resolution, and they cover 3175–5880 A with signal-to-noise ratios of 6–20 per 1.13 A pixel in the Lyα forest between Lyα and Lyβ. We show the continuum levels that we used in a previous paper to make a calibrated measurement of the amount of absorption in the Lyα forest at z = 1.9. We measure redshifts for 140 absorption-line systems, and we list the metal ions that we see in each system. We identify 526 emission lines and list their observed wavelengths, which we use to obtain new emission redshifts. We find that three emission lines, or line blends, in the forest have mean rest wavelengths of 1070.95 ± 1.00, 1123.13 ± 0.51, and 1175.88 ± 0.30 A.

Using Narrowband Photometry to Detect Young Brown Dwarfs in IC 348

We report the discovery of a population of young brown dwarf candidates in the open star cluster IC 348 and the development of a new spectroscopic classification technique using narrowband photometry. Observations were made using FLITECAM, the First Light Camera for SOFIA, at the 3 m Shane telescope at Lick Observatory. FLITECAM is a new 1-5 μm camera with an 8' field of view. Custom narrowband filters were developed to detect absorption features of water vapor (at 1.495 μm) and methane (at 1.66 μm) characteristic of brown dwarfs. These filters enable spectral classification of stars and brown dwarfs without spectroscopy. FLITECAM's narrow- and broadband photometry was verified by examining the color-color and color-magnitude characteristics of stars whose spectral type and reddening was known from previous surveys. Using our narrowband filter photometry method, it was possible to identify an object measured with a signal-to-noise ratio of 20 or better to within ±3 spectral class subtypes for late-type stars. With this technique, very deep images of the central region of IC 348 (H ~ 20.0) have identified 18 sources as possible L or T dwarf candidates. Out of these 18, we expect that between 3 and 6 of these objects are statistically likely to be background stars, the remainder being true low-mass members of the cluster. If confirmed as cluster members, then these are very low mass objects (~5MJup). We also describe how two additional narrowband filters can improve the contrast between M, L, and T dwarfs as well as provide a means to determine the reddening of an individual object.

Relative Flux Calibration of Keck HIRES Echelle Spectra11Based on data obtained with the Kast spectrograph on the Lick Observatory 3 m Shane telescope and with the HIRES and ESI spectrographs at the W. M. Keck Observatory, which is a joint facility of the University of California, the California Institute of Technology, and NASA.

ABSTRACTWe describe a method to calibrate the relative flux levels in spectra from the High‐Resolution Echelle Spectrograph (HIRES) on the Keck I telescope. Standard data reduction techniques that transfer the instrument response between HIRES integrations leave errors in the flux of 5%–10% because the effective response varies during the night. The flux errors are most severe near the ends of each spectral order, where there can be discontinuous jumps. The source of these errors is uncertain but may include changes in the vignetting connected to the optical alignment. Our flux calibration method uses a calibrated reference spectrum of each target to calibrate individual HIRES integrations. We determine the instrument response independently for each integration, and hence we avoid the need to transfer the instrument response between HIRES integrations. The procedure can be applied to any HIRES spectrum or any other spectrum. While the accuracy of the method depends upon many factors, we have been able to flux‐calibrate a HIRES spectrum to 1% over scales of 200 Å that include order joins. We illustrate the method with spectra of QSO 1243+3047, toward which we have measured the deuterium‐to‐hydrogen abundance ratio.

Emission Lines of [Clii] in the Optical Spectra of Gaseous Nebulae

Recent R-matrix calculations of electron impact excitation rates among the 3s23p4 levels of Cl II are used to derive the nebular emission-line intensity ratios R1 = I(6161.8 A)/I(8578.7 A) and R2 = I(6161.8 A)/I(9123.6 A) as a function of electron temperature (Te) and density (Ne). The ratios are found to be very sensitive to changes in Te but not Ne for densities lower than 105 cm-3. Hence, they should, in principle, provide excellent optical Te diagnostics for planetary nebulae. The observed values of R1 and R2 for the planetary nebulae NGC 6741 and IC 5117, measured from spectra obtained with the Hamilton echelle spectrograph on the 3 m Shane Telescope, imply temperatures in excellent agreement with those derived from other diagnostic lines formed in the same region of the nebula as [Cl II]. This provides some observational support for the accuracy of the [Cl II] line ratio calculations and hence the atomic data on which they are based. The [Cl II] 8578.7 and 9123.6 A lines are identified for the first time (to our knowledge) in a high-resolution spectrum of the symbiotic star RR Telescopii, obtained with the University College London Echelle Spectrograph on the 3.9 m Anglo-Australian Telescope. However, the 6161.8 A feature is unfortunately too weak to be identified in the RR Telescopii observations, consistent with its predicted line strength.

Characterizing the Adaptive Optics Off‐Axis Point‐Spread Function. I. A Semiempirical Method for Use in Natural Guide Star Observations1,1Based, in part, on observations obtained at the Lick Observatory, which is operated by the University of California. 22All authors except D. C. are affiliated with the Center for Adaptive Optics.

ABSTRACTEven though the technology of adaptive optics (AO) is rapidly maturing, calibration of the resulting images remains a major challenge. The AO point‐spread function (PSF) changes quickly in both time and position on the sky. In a typical observation, the star used for guiding will be separated from the scientific target by 10″–30″. This is sufficient separation to render images of the guide star by themselves nearly useless in characterizing the PSF at the off‐axis target position. A semiempirical technique is described that improves the determination of the AO off‐axis PSF. The method uses calibration images of dense star fields to determine the change in PSF with field position. It then uses this information to correct contemporaneous images of the guide star to produce a PSF that is more accurate for both the target position and the time of a scientific observation. We report on tests of the method using natural guide star AO systems on the Canada‐France‐Hawaii Telescope and Lick Observatory Shane Telescope, augmented by simple atmospheric computer simulations. At 25″ off‐axis, predicting the PSF FWHM using only information about the guide star results in an error of 60%. Using an image of a dense star field lowers this error to 33%, and our method, which also folds in information about the on‐axis PSF, further decreases the error to 19%.

New Distant Companions to Known Nearby Stars. I. GJ 4047B, GJ 718B, GJ 747.2C, GJ 4100B, and GJ 4153B

In an ongoing survey for high proper motion stars at low Galactic latitudes (-25° < b < 25°) in the Digitized Sky Survey, we have identified five previously uncataloged common proper motion companions to stars listed in the Preliminary Version of the Third Catalogue of Nearby Stars (GJ stars). For each system, the relative proper motion between the components is less than 5% of the common proper motion of the pair. Spectra of the pairs have been obtained at the Lick 3 m Shane Telescope, confirming that the systems are indeed wide-separation binaries. The systems are classified as follows: GJ 4047AB = K5 V + M5 V, GJ 718AB = K5 V + M4.5 V, GJ 747.2ABC = (K7 V + K7 V) + M4 Ve, GJ 4100AB = M1 V + M4.5 Ve, and GJ 4153AB = M0.5 V + M3.5 V. The total area surveyed contains 346 Gliese stars, which suggests that ≈1.5% of the stars listed in the Preliminary Version of the Third Catalogue of Nearby Stars have unrecognized proper motion companions. We predict that ≈15–50 more new distant companions to GJ stars will be discovered in the Digitized Sky Survey.

Young massive star clusters in M51

A search for young massive star clusters (YMCs) in the nearby face-on spiral galaxy M51 (NGC 5194) has been carried out using UBV CCD images from the prime focus camera on the Lick 3-m Shane telescope. The YMC population is found to be quite rich with a specific U-band luminosity consistent with the high current star formation rate (SFR) of this galaxy. The brightest clusters have far brighter than any young clusters currently known in the Milky Way and even surpassing the luminosity of the R136 cluster in the 30 Dor complex in the Large Magellanic Cloud. A few of the YMCs are examined on archive images from the Wide Field Planetary Camera (WF/PC2) on board the Hubble Space Telescope(HST), confirming their cluster nature and providing estimates of their effective radii of 2–3 pc. The number of YMCs in M51 is compatible with extrapolation of a power-law luminosity function with exponent ∼−2 from a Milky Way-like population of open clusters. Both the SFR and TL(U) of M51 are similar to those of other cluster-rich spiral galaxies like NGC 1313 and M83.

Emission lines of [K V] in the optical spectra of gaseous nebulae.

Recent R-matrix calculations of electron impact excitation rates in K v are used to derive the nebular emission line ratio R = I(4122.6 A)/I(4163.3 A) as a function of electron density (N(e)). This ratio is found to be very sensitive to changes in N(e) over the density range 10(3) to 10(6) cm(-3), but does not vary significantly with electron temperature, and hence in principle should provide an excellent optical N(e) diagnostic for the high-excitation zones of nebulae. The observed value of R for the planetary nebula NGC 7027, measured from a spectrum obtained with the Hamilton Echelle spectrograph on the 3-m Shane Telescope, implies a density in excellent agreement with that derived from [Ne iv], formed in the same region of the nebula as [K v]. This observation provides observational support for the accuracy of the theoretical [K v] line ratios, and hence the atomic data on which they are based. However, the analysis of a high-resolution spectrum of the symbiotic star RR Telescopii, obtained with the University College London Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope, reveals that the [K v] 4122.6 A line in this object is badly blended with Fe ii 4122.6 A. Hence, the [K v] diagnostic may not be used for astrophysical sources that show a strong Fe ii emission line spectrum.

Spectroscopic Observation of the Planetary Nebula IC 4846

ABSTRACTA high‐dispersion optical (3700–10100 Å) spectrum was secured with the Hamilton echelle spectrograph at the coudé focus of the 120 inch (3 m) Shane telescope at Lick Observatory, with the goal of deriving chemical abundances for the compact planetary nebula IC 4846. We also remeasured the UV spectra from the IUE archive. Diagnostics indicate that the entire planetary nebula may be represented by an electron density Nϵ≃9000 cm−3 and electron temperature Tϵ≃10,500 K. However, diagnostics seem to imply that the [O ii] and [S ii] zone electron temperatures are higher than the [O iii] radiating strata. The electron density of the [O ii] and [S ii] zone might be higher as well (for which Nϵ≃20,000 cm−3). The photoionization model, which represents most of the observed line intensities, seems to confirm this physical condition, although the actual situation may be much more complicated. On the basis of the semiempirical ionization correction method and the photoionization model calculation, we derived the chemical abundances in this planetary nebula. Our optical data were compared with the image‐tube scanner data from Aller & Czyzak. Apparently, there is a long‐term spectral line variation in IC 4846. Chemical abundances derived in the present study agree, within 30%, with those previously estimated in Aller & Czyzak, except for carbon; the C, N, O, and Ne ratios are lower than both the average planetary nebula and the solar abundance. IC 4846 is a metal‐deficient planetary nebula that may have evolved from a Population II progenitor.