19 research outputs found
The Carnegie Hubble Program
We present an overview of and preliminary results from an ongoing
comprehensive program that has a goal of determining the Hubble constant to a
systematic accuracy of 2%. As part of this program, we are currently obtaining
3.6 micron data using the Infrared Array Camera (IRAC) on Spitzer, and the
program is designed to include JWST in the future. We demonstrate that the
mid-infrared period-luminosity relation for Cepheids at 3.6 microns is the most
accurate means of measuring Cepheid distances to date. At 3.6 microns, it is
possible to minimize the known remaining systematic uncertainties in the
Cepheid extragalactic distance scale. We discuss the advantages of 3.6 micron
observations in minimizing systematic effects in the Cepheid calibration of the
Hubble constant including the absolute zero point, extinction corrections, and
the effects of metallicity on the colors and magnitudes of Cepheids. We are
undertaking three independent tests of the sensitivity of the mid-IR Cepheid
Leavitt Law to metallicity, which when combined will allow a robust constraint
on the effect. Finally, we are providing a new mid-IR Tully-Fisher relation for
spiral galaxies
Cool Companions to White Dwarf Stars from the Two Micron All Sky Survey All Sky Data Release
We present the culmination of our near-infrared survey of the optically spectroscopically identified white dwarf stars from the McCook and Sion catalog, conducted using photometric data from the Two Micron All Sky Survey final All Sky Data Release. The color selection technique, which identifies candidate binaries containing a white dwarf and a low-mass stellar (or substellar) companion via their distinctive locus in the near-infrared color-color diagram, is demonstrated to be simple to apply and to yield candidates with a high rate of subsequent confirmation. We recover 105 confirmed binaries, and identify 27 firm candidates (19 of which are new to this work) and 21 tentative candidates (17 of which are new to this work) from the 2MASS data. Only a small number of candidates from our survey have likely companion spectral types later than M5, none of which is an obvious L-type (i.e., potential brown dwarf) companion. Only one previously known white dwarf + brown dwarf binary is detected. This result is discussed in the context of the 2MASS detection limits, as well as other recent observational surveys that suggest a very low rate of formation (or survival) for binary stars with extreme mass ratios
The Cepheid Period-Luminosity Relation at Mid-Infrared Wavelengths: I. First-Epoch LMC Data
We present the first mid-infrared Period-Luminosity (PL) relations for Large
Magellanic Cloud (LMC) Cepheids. Single-epoch observations of 70 Cepheids were
extracted from Spitzer IRAC observations at 3.6, 4.5, 5.8 and 8.0 microns,
serendipitously obtained during the SAGE (Surveying the Agents of a Galaxy's
Evolution) imaging survey of the LMC. All four mid-infrared PL relations have
nearly identical slopes over the period range 6 - 88 days, with a small scatter
of only +/-0.16 mag independent of period for all four of these wavelengths. We
emphasize that differential reddening is not contributing significantly to the
observed scatter, given the nearly two orders of magnitude reduced sensitivity
of the mid-IR to extinction compared to the optical. Future observations,
filling in the light curves for these Cepheids, should noticeably reduce the
residual scatter. These attributes alone suggest that mid-infrared PL relations
will provide a practical means of significantly improving the accuracy of
Cepheid distances to nearby galaxies.Comment: 19 pages, 4 figures, 1 table, Accepted for publication in the
Astrophysical Journa
The Cepheid Period-Luminosity Relation at Mid-Infrared Wavelengths: II. Second-Epoch LMC Data
We present revised and improved mid-infrared Period-Luminosity (PL) relations
for Large Magellanic Cloud (LMC) Cepheids based on double-epoch data of 70
Cepheids observed by Spitzer at 3.6, 4.5, 5.8 and 8.0um. The observed scatter
at all wavelengths is found to decrease from +/-0.17 mag to +/-0.14 mag, which
is fully consistent with the prediction that the total scatter is made up of
roughly equal contributions from random sampling of the light curve and
nearly-uniform samplings of stars across the instability strip. It is
calculated that the Cepheids in this sample have a full amplitude of about 0.4
mag and that their fully-sampled, time-averaged magnitudes should eventually
reveal mid-infrared PL relations that each have intrinsic scatter at most at
the +/-0.12 mag level, and as low as +/-0.08 mag after correcting for the tilt
of the LMC.Comment: 7 pages, 6 figures, 1 data tabl
Erratum: The Carnegie Hubble Program: The Leavitt Law at 3.6 micron and 4.5 micron in the Large Magellanic Cloud (2011, APJ, 743, 76)
Due to an error at the publisher, an incorrect version of Table 3 appeared in the published article. The updated version of
Table 3 is given
The Cepheid Period-Luminosity Relation (The Leavitt Law) at Mid-Infrared Wavelengths: III. Cepheids in NGC 6822
We present the first application of mid-infrared Period-Luminosity relations
to the determination of a Cepheid distance beyond the Magellanic Clouds. Using
archival IRAC imaging data on NGC 6822 from Spitzer we were able to measure
single-epoch magnitudes for sixteen long-period (10 to 100-day) Cepheids at
3.6um, fourteen at 4.5um, ten at 5.8um and four at 8.0um. The measured slopes
and the observed scatter both conform to the relations previously measured for
the Large Magellanic Cloud Cepheids, and fitting to those relations gives
apparent distance moduli of mod{3.6} = 23.57 +/- 0.06, mod{4.5} = 23.55 +/-
0.07, mod{5.8} = 23.60 +/- 0.09 and mod{8.0} = 23.51 +/-0.08 mag. A
multi-wavelength fit to the new IRAC moduli, and previously published BVRIJHK
moduli, allows for a final correction for interstellar reddening and gives a
true distance modulus of 23.49 +/- 0.03 mag with E(B-V) = 0.26 mag,
corresponding to a metric distance of 500 +/-8 kpc.Comment: Accepted to ApJ, 2 figure
The Cepheid Period-Luminosity Relation (The Leavitt Law) at Mid-Infrared Wavelengths: IV. Cepheids in IC 1613
We present mid-infrared Period-Luminosity relations for Cepheids in the Local
Group galaxy IC1613. Using archival IRAC imaging data from Spitzer we were able
to measure single-epoch magnitudes for five, 7 to 50-day, Cepheids at 3.6 and
4.5 microns. When fit to the calibrating relations, measured for the Large
Magellanic Cloud Cepheids, the data give apparent distance moduli of 24.29 +/-
0.07 and 24.28 +/- 0.07 at 3.6 and 4.5 microns, respectively. A
multi-wavelength fit to previously published BVRIJHK apparent moduli and the
two IRAC moduli gives a true distance modulus of 24.27 +/- 0.02 mag with E(B-V)
= 0.08 mag, and a corresponding metric distance of 715 kpc. Given that these
results are based on single-phase observations derived from exposures having
total integration times of only 1,000 sec/pixel we suggest that Cepheids out to
about 2 Mpc are accessible to Spitzer with modest integration times during its
warm mission. We identify the main limiting factor to this method to be
crowding/contamination induced by the ubiquitous population of infrared-bright
AGB stars.Comment: Accepted to ApJ December 2008: 9 pages, 3 figure
The Carnegie Hubble Program: The Leavitt Law at 3.6 \mu m and 4.5 \mu m in the Large Magellanic Cloud
The Carnegie Hubble Program (CHP) is designed to improve the extragalactic
distance scale using data from the post-cryogenic era of Spitzer. The ultimate
goal is a determination of the Hubble constant to an accuracy of 2%. This paper
is the first in a series on the Cepheid population of the Large Magellanic
Cloud, and focusses on the period-luminosity relations (Leavitt laws) that will
be used, in conjunction with observations of Milky Way Cepheids, to set the
slope and zero--point of the Cepheid distance scale in the mid-infrared. To
this end, we have obtained uniformly-sampled light curves for 85 LMC Cepheids,
having periods between 6 and 140 days. Period-luminosity and period-color
relations are presented in the 3.6 \mu m and 4.5\mu m bands. We demonstrate
that the 3.6 \mu m band is a superb distance indicator. The cyclical variation
of the [3.6]-[4.5] color has been measured for the first time. We attribute the
amplitude and phase of the color curves to the dissociation and recombination
of CO molecules in the Cepheid's atmosphere. The CO affects only the 4.5 \mu m
flux making it a potential metallicity indicator.Comment: 38 pages, 9 figures, 3 tables. ApJ accepted. Cepheid photometry
available in electronic version of ApJ, or on request from V
The Carnegie Supernova Project: First Near-Infrared Hubble Diagram to z~0.7
The Carnegie Supernova Project (CSP) is designed to measure the luminosity
distance for Type Ia supernovae (SNe Ia) as a function of redshift, and to set
observational constraints on the dark energy contribution to the total energy
content of the Universe. The CSP differs from other projects to date in its
goal of providing an I-band {rest-frame} Hubble diagram. Here we present the
first results from near-infrared (NIR) observations obtained using the Magellan
Baade telescope for SNe Ia with 0.1 < z < 0.7. We combine these results with
those from the low-redshift CSP at z <0.1 (Folatelli et al. 2009). We present
light curves and an I-band Hubble diagram for this first sample of 35 SNe Ia
and we compare these data to 21 new SNe Ia at low redshift. These data support
the conclusion that the expansion of the Universe is accelerating. When
combined with independent results from baryon acoustic oscillations (Eisenstein
et al. 2005), these data yield Omega_m = 0.27 +/- 0.0 (statistical), and
Omega_DE = 0.76 +/- 0.13 (statistical) +/- 0.09 (systematic), for the matter
and dark energy densities, respectively. If we parameterize the data in terms
of an equation of state, w, assume a flat geometry, and combine with baryon
acoustic oscillations, we find that w = -1.05 +/- 0.13 (statistical) +/- 0.09
(systematic). The largest source of systematic uncertainty on w arises from
uncertainties in the photometric calibration, signaling the importance of
securing more accurate photometric calibrations for future supernova cosmology
programs. Finally, we conclude that either the dust affecting the luminosities
of SNe Ia has a different extinction law (R_V = 1.8) than that in the Milky Way
(where R_V = 3.1), or that there is an additional intrinsic color term with
luminosity for SNe Ia independent of the decline rate.Comment: 44 pages, 23 figures, 9 tables; Accepted for publication in the
Astrophysical Journa