Arlo U. Landolt

Louisiana State University, Baton Rouge, Louisiana, United States

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Publications (22)73.37 Total impact

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    Ralph C. Bohlin, Arlo U. Landolt
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    ABSTRACT: Multicolor photometric data are presented for the CALSPEC stars P177D and P330E. Together with previously published photometry for nine other CALSPEC standards, the photometric observations and synthetic photometry from HST/STIS spectrophotometry agree in the B, V, R, and I bands to better than $\sim$1\% (10 mmag).
  • James L. Clem, Arlo U. Landolt
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    ABSTRACT: High-quality CCD-based UBVRI photometry is presented for ~45, 000 stars distributed among 60 different fields centered on the celestial equator and at δ –50°. This photometry has been calibrated to the standard Johnson UBV and Kron-Cousins RI systems via observations of the UBVRI standard stars presented in the works of Landolt. The majority of the stars in our photometric catalog fall in the magnitude range 12 V 22 and in the color range –0.3 (B – V) 1.8. Each star averages 67 measures in each UBVRI filter from data taken on 250 different photometric nights over a period of ~6.5 yr from two different telescopes. Our final photometric database effectively extends the UBVRI standard star network defined by Landolt to much fainter magnitudes and increases the number density of stars within pre-existing standard fields. Hence, these new, fainter standards serve as suitable calibrators for investigators who employ either small or large-aperture telescopes for their observational projects.
    The Astronomical Journal 09/2013; 146(4):88. DOI:10.1088/0004-6256/146/4/88 · 4.97 Impact Factor
  • James L. Clem, Arlo U. Landolt
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    ABSTRACT: We present extensive time-series photometry confirming that two stars located in the field of PG 1047 + 0031047+003 are short-period eclipsing binary systems. One of these stars, published as a photometric standard by Landolt and designated as PG 1047 + 003C1047+003C, is shown to have eclipse depths on the order of 0.1 mag and a period of ∼0.28∼0.28 days. The other star, located ∼2 ′′ ∼2′′ south-southwest of PG 1047 + 0031047+003, exhibits a similar amplitude and light-curve shape, but has a slightly longer period of ∼0.35∼0.35 days. Light-curve solutions for both variables, based on the Wilson-Devinney code, reveal them to be contact binaries with low inclinations and each possessing uneven maxima, which we attribute to the presence of a single hot spot on the surfaces of the primary stars.
    Publications of the Astronomical Society of the Pacific 06/2012; 59(6):535-544. DOI:10.1086/666494 · 3.23 Impact Factor
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    ABSTRACT: We report the discovery by M. Linnolt on JD 2455665.7931 (UT 2011 April 14.29) of the sixth eruption of the recurrent nova T Pyxidis. This discovery was made just as the initial fast rise was starting, so with fast notification and response by observers worldwide, the entire initial rise was covered (the first for any nova), and with high time resolution in three filters. The speed of the rise peaked at 9 mag/day, while the light curve is well fit over only the first two days by a model with a uniformly expanding sphere. We also report the discovery by R. Stubbings of a pre-eruption rise starting 18 days before the eruption, peaking 1.1 mag brighter than its long-time average, and then fading back towards quiescence 4 days before the eruption. This unique and mysterious behavior is only the fourth known anticipatory rise closely spaced before a nova eruption. We present 19 timings of photometric minima from 1986 to February 2011, where the orbital period is fast increasing with P/dot{P}=313,000 yrs. From 2008-2011, T Pyx had a small change in this rate of increase, so that the orbital period at the time of eruption was 0.07622950+-0.00000008 days. This strong and steady increase of the orbital period can only come from mass transfer, for which we calculate a rate of 1.7-3.5x10^-7 Mo/yr. We report 6116 magnitudes between 1890 and 2011, for an average B=15.59+-0.01 from 1967-2011, which allows for an eruption in 2011 if the blue flux is nearly proportional to the accretion rate. The ultraviolet-optical-infrared spectral energy distribution is well fit by a power law with flux proportional to nu^1.0, although the narrow ultraviolet region has a tilt with a fit of \nu^{1/3}. We prove that most of the T Pyx light is not coming from a disk, or any superposition of blackbodies, but rather is coming from some nonthermal source.
    The Astrophysical Journal 08/2011; 773(1). DOI:10.1088/0004-637X/773/1/55 · 6.28 Impact Factor
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    ABSTRACT: SN 2010jl was an extremely bright, Type IIn supernova (SN) which showed a significant infrared (IR) excess no later than 90 days after explosion. We have obtained Spitzer 3.6 and 4.5 μm and JHK observations of SN 2010jl ~90 days post-explosion. Little to no reddening in the host galaxy indicated that the circumstellar material lost from the progenitor must lie in a torus inclined out of the plane of the sky. The likely cause of the high mid-IR flux is the reprocessing of the initial flash of the SN by pre-existing circumstellar dust. Using a three-dimensional Monte Carlo radiative-transfer code, we have estimated that between 0.03 and 0.35 M ☉ of dust exists in a circumstellar torus around the SN located 6 × 1017 cm away from the SN and inclined between 60° and 80° to the plane of the sky. On day 90, we are only seeing the illumination of approximately 5% of this torus, and expect to see an elevated IR flux from this material up until day ~ 450. It is likely this dust was created in a luminous blue variable (LBV) like mass-loss event of more than 3 M ☉, which is large but consistent with other LBV progenitors such as η Carinae.
    The Astronomical Journal 06/2011; 142(2):45. DOI:10.1088/0004-6256/142/2/45 · 4.97 Impact Factor
  • Arlo U. Landolt, J. L. Clem
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    ABSTRACT: Photometric programs doable, and accuracies achievable with the CTIO 1.0-m telescope's CCD system, Y4KCam, will be discussed. This program is supported by the National Science Foundation.
  • Arlo U. Landolt
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    ABSTRACT: This paper will explore the implementation of the photometric system established by Harold Johnson and colleagues, and the accuracies that have been achieved through its use.
    04/2011: pages 109-125;
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    ABSTRACT: We present the results of a deep, wide-field CCD survey for the open cluster NGC~3532. Our new $BV(RI)_{c}$ photometry effectively covers a one square degree area and reaches an unprecedented depth of $V\sim21$ to reveal that NGC~3532 is a rich open cluster that harbors a large number of faint, low-mass stars. We employ a number of methods to reduce the impact of field star contamination in the cluster color-magnitude diagrams, including supplementing our photometry with $JHK_{s}$ data from the 2MASS catalog. These efforts allow us to define a robust sample of candidate main sequence stars suitable for a purely empirical determination of the cluster's parameters by comparing them to the well-established Hyades main sequence. Our results confirm previous findings that NGC~3532 lies fairly near to the Sun [$(m-M)_0=8.46\pm0.05$; $492^{+12}_{-11}$~pc] and has an extremely low reddening for its location near the Galactic plane [$E(B-V)=0.028\pm0.006$]. Moreover, an age of $\sim300$\,Myr has been derived for the cluster by fitting a set of overshooting isochrones to the well-populated upper main-sequence. This new photometry also extends faint enough to reach the cluster white dwarf sequence, as confirmed by our photometric recovery of eight spectroscopically identified members of the cluster. Using the location of these eight members, along with the latest theoretical cooling tracks, we have identified $\sim30$ additional white dwarf stars in the $[V,~(B-V)]$ color-magnitude diagram that have a high probability of belonging to NGC~3532. The age we derive from fitting white dwarf isochrones to the locus of these stars, $300\pm100$\,Myr, is consistent with the age derived from the turnoff. Our analysis of the photometry also includes an estimation of the binary star fraction, as well as a determination of the cluster's luminosity and mass functions.
    The Astronomical Journal 01/2011; DOI:10.1088/0004-6256/141/4/115 · 4.97 Impact Factor
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    ABSTRACT: We report on the 2010 eruption of the recurrent nova U Scorpii. This outburst was predicted in 2005 and discovered independently by AAVSO observers Barbara G. Harris and Shawn Dvorak on 28 January 2010 as a result of a monitoring program coordinated by our group at LSU in conjunction with the AAVSO. The eruption lasted approximately 64 days, over the course of which more than 35,000 pre-arranged and serendipitous observations were made in all wavelengths from radio to X-ray. We present multi-wavelength light curves (UBVRIJHKby+UV+X-ray) of the entire eruption which show the overall speed of the event, the expected first plateau, the unexpected second plateau, and the return to quiescence. As anticipated, the onset of the optical plateau coincided with the turn-on of the supersoft X-ray emission and the reemergence of the eclipses. Our comprehensive coverage shows fine-scale phenomena as well, such as flares of up to 0.5 mag in amplitude during the initial fast decline which are as yet unexplained and late aperiodic dips (distinct from the well-known eclipses) that are likely caused by raised rims on the re-forming accretion disk. Additionally, we present outburst spectra showing unusual features such as very high expansion velocities (on the order of 10,000 km/s) and castellated (triple-peaked) Balmer line profiles. This work was funded in part by NSF Grant AST-0708079.
  • Arlo U. Landolt, John L. Africano
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    ABSTRACT: UBV broadband photometry is reported for 19 stars in the direction of the Galactic (open) star clusters NGC 1746/1750/1758. Nine of these stars possess proper motions that point to the existence of a group centered at α=0504 and δ=+23°43.5. One known variable star, V1153 Tau, is recovered, and an emission-line star, HD 32318, is shown to be a variable star. RT Tau is reconfirmed to be constant in light.
    Publications of the Astronomical Society of the Pacific 09/2010; 122(895):1008-1014. DOI:10.1086/656322 · 3.23 Impact Factor
  • Arlo U. Landolt, James L. Clem
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    ABSTRACT: Telescope time is being requested for continued enhancement and development of broad-band (UBVRI) CCD photometric standard stars. Use of such standard stars permits the combination and inter-comparison of the brightness and color measurements of celestial phenomena made by different investigators with different sets of equipment, on land or in space. The continued efforts at improving the broad-band UBVRI photometric system is important so that all astronomers using and needing photometric results can be confident of the zero points, transformations, and systematics of their results. This work also will allow the intercomparison of UBVRI and SDSS photometry in common fields. The stars and fields upon which observational work will continue are distributed around the celestial equator, as well as in a zone centered at -50 degrees declination. Standard star publications by the author are some of the most heavily referenced articles in astronomy. There is no doubt but that the photometric sequences being established via this observing proposal also will see extensive use.
  • Arlo U. Landolt, James L. Clem
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    ABSTRACT: The star R CrB has been monitored at its faintest known minimum brightness in a search for possible light variations. No short-term variations were identified. In addition, photometry is presented for stars in the surrounding neighborhood.
    Publications of the Astronomical Society of the Pacific 05/2010; 122(891):541-548. DOI:10.1086/653126 · 3.23 Impact Factor
  • James L. Clem, Arlo U. Landolt
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    ABSTRACT: The star PG 1323-086A (GSC 05544-00493) is shown to be a short-period eclipsing binary system. Photometric elements for the system are computed and reveal that the stellar components are in a marginal degree of contact (f˜8%) with a small temperature difference of about 700 K. During the study of the starfield, a nearby object, HE 1323-0830, was also discovered to be variable in light. This star has been cataloged as a candidate blue straggler and is most likely a pulsating variable.
    Publications of the Astronomical Society of the Pacific 01/2010; 122:27-34. DOI:10.1086/649852 · 3.23 Impact Factor
  • Arlo U. Landolt, James L. Clem
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    ABSTRACT: Telescope time is being requested for continued enhancement and development of broad-band (UBVRI) CCD photometric standard stars. Use of such standard stars permits the combination and inter-comparison of the brightness and color measurements of celestial phenomena made by different investigators with different sets of equipment, on land or in space. The continued efforts at improving the broad-band UBVRI photometric system is important so that all astronomers using and needing photometric results can be confident of the zero points, transformations, and systematics of their results. This work also will allow the intercomparison of UBVRI and SDSS photometry in common fields. The KPNO observing will take advantage of the availability of a larger telescope, the 2.1-m, than is available at CTIO. The stars and fields upon which observational work will continue are distributed around the celestial equator, as well as in a zone centered at +45 degrees declination. Standard star publications by the author are some of the most heavily referenced in astronomy. There is no doubt but that the photometric sequences being established via this observing proposal also will see extensive use.
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    Arlo U. Landolt
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    ABSTRACT: New broadband UBVRI photoelectric observations on the Johnson-Kron-Cousins photometric system have been made of 202 stars around the sky, and centered at the celestial equator. These stars constitute both an update of and additions to a previously published list of equatorial photometric standard stars. The list is capable of providing, for both celestial hemispheres, an internally consistent homogeneous broadband standard photometric system around the sky. When these new measurements are included with those previously published by Landolt (1992), the entire list of standard stars in this paper encompasses the magnitude range 8.90 < V < 16.30, and the color index range -0.35 < (B - V) < +2.30. Comment: 66 pages, 11 figures; complete version (including finding charts) to appear in May issue of AJ (2009, 137, 4186)
    The Astronomical Journal 04/2009; DOI:10.1088/0004-6256/137/5/4186 · 4.97 Impact Factor
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    ABSTRACT: We present an exhaustive quantitative comparison of all the known extinction curves in the Small and Large Magellanic Clouds (SMC and LMC) with our understanding of the general behavior of Milky Way extinction curves. The RV-dependent CCM relationship of Cardelli, Clayton, and Mathis and the sample of extinction curves used to derive this relationship are used to describe the general behavior of Milky Way extinction curves. The ultraviolet portion of the SMC and LMC extinction curves are derived from archival IUE data, except for one new SMC extinction curve, which was measured using Hubble Space Telescope Space Telescope Imaging Spectrograph observations. The optical extinction curves are derived from new ( for the SMC) and literature UBVRI photometry ( for the LMC). The near-infrared extinction curves are calculated mainly from 2MASS photometry supplemented with DENIS and new JHK photometry. For each extinction curve, we give R(V) = A(V)/E(B - V) and N(H I) values that probe the same dust column as the extinction curve. We compare the properties of the SMC and LMC extinction curves with the CCM relationship three different ways: each curve by itself, the behavior of extinction at different wavelengths with RV, and the behavior of the extinction curve Fitzpatrick and Massa fit parameters with RV. As has been found previously, we find that a small number of LMC extinction curves are consistent with the CCM relationship, but the majority of the LMC and all the SMC curves do not follow the CCM relationship. For the first time, we find that the CCM relationship seems to form a bound on the properties of all the LMC and SMC extinction curves. This result strengthens the picture dust extinction curves exhibit of a continuum of properties between those found in the Milky Way and the SMC bar. Tentative evidence based on the behavior of the extinction curves with dust-to-gas ratio suggests that the continuum activity.
    The Astrophysical Journal 12/2008; 594(1):279. DOI:10.1086/376774 · 6.28 Impact Factor
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    ABSTRACT: We present well-sampled optical (UBVRI) and infrared (JHK) light curves of the nearby (≈18.0 Mpc) Type Ia supernova SN 2001el, from 11 days before to 142 days after the time of B-band maximum. The data represent one of the best sets of optical and infrared photometry ever obtained for a Type Ia supernova (SN). Based on synthetic photometry using optical spectra of SN 2001el and optical and infrared spectra of SN 1999ee, we were able to devise filter corrections for the BVJHK photometry of SN 2001el, which to some extent resolve systematic differences between SN 2001el data sets obtained with different telescope/filter/instrument combinations. We also calculated V-minus-infrared color curves on the basis of a delayed detonation model and show that the theoretical color curves match the unreddened loci for Type Ia SNe with midrange decline rates to within 0.2 mag. Given the completeness of the light curves and the elimination of filter-oriented systematic errors to some degree, the data presented here will be useful for the construction of photometric templates, especially in the infrared. On the whole the photometric behavior of SN 2001el was quite normal. The second H-band maximum being brighter than the first H-band maximum is in accord with the prediction of Krisciunas et al. for Type Ia SNe with midrange decline rates. The photometry exhibits nonzero host extinction, with total AV = 0.57 ± 0.05 mag along the line of sight. NGC 1448, the host of SN 2001el, would be an excellent target for a distance determination using Cepheids.
    The Astronomical Journal 12/2007; 125(1):166. DOI:10.1086/345571 · 4.97 Impact Factor
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    George W. Preston, Arlo U. Landolt
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    ABSTRACT: The blue metal-poor (BMP) star CS 22966-043 is an SX Phoenicis star and the primary of a spectroscopic binary with a provisional orbital period of ~430 days. Radial velocity and UBV photometric observations of this star made in 1998 require downward revision of the orbital period to 319 days. The BMP star CS 29499-057 also appears to be an SX Phoenicis star with small amplitude (ΔV ~ 0.04 mag) and short period (P = 0.0417 days), on the basis of photometric and radial velocity observations obtained in 1998. There is some indication that it too may be the primary of a spectroscopic binary. Three other BMP stars have radial velocity standard deviations greater than those of 17 BMP radial velocity standards. We suggest that they may be small-amplitude SX Phoenicis stars. Finally, the BMP star CS 29497-017 is shown to be a short-period velocity variable (P = 0.302 days) on the basis of observations accumulated over an interval of 2200 days, but we were unable to detect a light variation in 1998 July. Therefore, the nature of the velocity variation of this object remains uncertain.
    The Astronomical Journal 12/2007; 118(6):3006. DOI:10.1086/301133 · 4.97 Impact Factor
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    Arlo U. Landolt, Alan K. Uomoto
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    ABSTRACT: Photoelectric data on the Johnson-Kron-Cousins UBVRI broadband photometric system are provided for a set of stars which have been used as spectrophotometric standard stars at the Hubble Space Telescope. Comment: 76 pages, 48 figures - published version available here: http://www.journals.uchicago.edu/AJ/journal/issues/v133n3/205588/205588.html . Also see ERRATUM at: http://www.journals.uchicago.edu/AJ/journal/issues/v133n5/205838/205838.html
    The Astronomical Journal 04/2007; 133(3). DOI:10.1086/510485 · 4.97 Impact Factor
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    Arlo U. Landolt
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    ABSTRACT: UBVRI photoelectric observations have been made of 109 stars around the sky, centered more or less at -50 degrees declination. The majority of the stars fall in the magnitude range 10.4 < V < 15.5 and in the color index range -0.33 < (B - V) < +1.66. These new broadband photometric standard stars average 16.4 measurements each from data taken on 116 different nights over a period of 4 yr. Similar data are tabulated for 19 stars of interest that were not observed often enough to make them well-defined standard stars. Comment: 80 pages, 57 figures - published version available here: http://www.journals.uchicago.edu/AJ/journal/issues/v133n6/205795/205795.html
    The Astronomical Journal 04/2007; 133(6). DOI:10.1086/518000 · 4.97 Impact Factor

Publication Stats

458 Citations
73.37 Total Impact Points

Institutions

  • 2007–2012
    • Louisiana State University
      • Department of Physics & Astronomy
      Baton Rouge, Louisiana, United States
  • 2002
    • University of Nottingham
      • School of Chemistry
      Nottigham, England, United Kingdom