Arlo U. Landolt

UBVRI photometric standard stars in the magnitude range 11.5-16.0 around the celestial equator

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A Quantitative Comparison of the Small Magellanic Cloud, Large Magellanic Cloud, and Milky Way Ultraviolet to Near-Infrared Extinction Curves*

We present an exhaustive, quantitative comparison of all of 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 R_V dependent CCM relationship and the sample of extinction curves used to derive this relationship is 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 HST/STIS 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(HI) values which 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 R_V, and behavior of the extinction curve FM fit parameters with R_V. As has been found previously, we find that a small number of LMC extinction curves are consistent with the CCM relationship, but majority of the LMC and all of 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 of the LMC and SMC extinction curves. This result strengthens the picture of dust extinction curves exhibit a continuum of properties between those found in the Milky Way and the SMC Bar. (abridged)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 RV = 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 of dust extinction curves is possibly caused by the environmental stresses of nearby star formation activity.

Broadband UBVRI photometry of the baldwin-Stone southern hemisphere spectrophotometric standards

Photoelectric broadband UBVRI data on the Johnson-Kron-Cousins photometric system are presented for the Baldwin-Stone southern hemisphere secondary spectrophotometric standard stars

UBVRI PHOTOMETRIC STANDARD STARS AROUND THE CELESTIAL EQUATOR: UPDATES AND ADDITIONS

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.

Optical and Infrared Photometry of the Nearby Type Ia Supernova 2001el

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.

Optical Multicolor Photometry of Spectrophotometric Standard Stars

Photoelectric data on the Johnson-Kron-Cousins UBVRI broadband photometric system are provided for a set of stars that have been used as spectrophotometric standard stars for the Hubble Space Telescope.

Starcounts Redivivus. III. A Possible Detection of the Sagittarius Dwarf Spheroidal Galaxy at b = ?40?

As part of the Selected Areas Starcounts Survey, a CCD survey to V > 21, we have obtained VI photometry of two fields at b = ?40? aligned roughly with an extrapolation of the major axis of the Sagittarius dwarf spheroidal galaxy. Comparison of the color-magnitude diagram (CMD) for some of these fields with the CMDs of fields reflected about the Galactic l = 0? meridian reveals an excess of stars at V0 = 17.85 and 0.9 < (V-I)0 < 1.1 in the (l, b) = (11?, -40?) field. The excess stars have colors consistent with the Sgr red clump, and deeper CMD imaging in these locations shows evidence of a main-sequence turnoff (MSTO) at V = 21, with the main sequence extending to the limit of our data (V = 24). The surface brightnesses we derive from either the potential excess of red clump stars or the apparent excess of MSTO stars are consistent with each other and with the results of other surveys at this latitude. No similar excess appears in our northern Galactic hemisphere fields near the (l, b) = (353?, +41?) field. We have obtained spectroscopy of all 30 candidate red clump stars in the range 0.9 < (V-I)0 < 1.1and 17.75 < V0 < 17.95. The radial velocity distribution of the stars, while dissimilar from expectations of Galactic structure models, does not show a contribution by stars near the Galactocentric radial velocity seen in other studies near the Sgr core. It is difficult to reconcile a photometric result that is consistent with other explorations of the Sagittarius stream with a radial velocity distribution that is apparently inconsistent. In a companion paper, we discuss how some of the discrepancies are resolved if our potential Sgr detection corresponds to a different Sgr tidal streamer than that detected by most other surveys.

UBVRI Photometric Standard Stars around the Sky at −50° Declination

UBVRI photoelectric observations have been made of 109 stars around the sky, centered more or less at -50° 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.

The optical light curves of SN 1980N and SN 1981D in NGC 1316 (Fornax A)

Optical photometry of the two supernovae, 1980N and 1981D, which appeared in the peculiar D-type galaxy NGC 1316 (Fornax A) is presented. These data are combined with published observations to produce definitive optical light curves. It is found that the maximum-light magnitudes of both supernovae were the same to within ± 0.1 mag, in agreement with infrared light curve observations. The shapes of the UBV light curves of the best observed of the two supernovae, 1980N, closely resembled those of the type Ia prototype SN 1981B. It is also shown that an optical spectrum of SN 1980N taken 30 days after B maximum was virtually identical to a spectrum of SN 1981B obtained at the same point in its evolution

Evidence for Pre-existing Dust in the Bright Type IIn SN 2010jl

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.