The Impact of Observing Strategy on the Reliable Classification of Standard Candle Stars: Detection of Amplitude, Period, and Phase Modulation (Blazhko Effect) of RR Lyrae Stars with LSST

The Vera C. Rubin Observatory will carry out its Legacy Survey of Space and Time (LSST) with a single-exposure depth of r ∼ 24.7 and an anticipated baseline of 10 yr, allowing access to the Milky Way’s old halo not only deeper than, but also with a longer baseline and better cadence than, e.g., PS1 3π. This will make the LSST ideal to study populations of variable stars such as RR Lyrae stars (RRL). Here, we address the question of observing strategy optimization of LSST, as survey footprint definition, single-visit exposure time, as well as the cadence of repeat visits in different filters are yet to be finalized. We present metrics used to assess the impact of different observing strategies on the reliable detectability and classification of standard candle variable stars, including detection of amplitude, period, and phase modulation effects of RRL (the so-called Blazhko effect), by evaluating metrics for simulated potential survey designs. So far, due to the depths and cadences of typical all-sky surveys, it has been nearly impossible to study this effect on a larger sample. All-sky surveys with relatively few observations over a moderately long baseline allow only for fitting phase-folded RRL light curves, thus integrating over the complete survey length and hiding any information regarding possible period or phase modulation during the survey. On the other hand, surveys with cadences fit to detect slightly changing light curves usually have a relatively small footprint. LSST’s survey strategy, however, will allow for studying variable stars in a way that makes population studies possible.

Calibration of Surface Brightness Fluctuations for Dwarf Galaxies in the Hyper Suprime-Cam gi Filter System

Surface brightness fluctuation (SBF) magnitudes are a powerful standard candle to measure distances to semiresolved galaxies in the local universe, a majority of which are dwarf galaxies that often have bluer colors than bright early-type galaxies. We present an empirical i-band SBF calibration in a blue regime, 0.2 ≲ (g − i)0 ≲ 0.8 in the Hyper Suprime-Cam (HSC) magnitude system. We measure SBF magnitudes for 12 nearby dwarf galaxies of various morphological types with archival HSC imaging data, and use their tip of the red giant branch distances to derive fluctuation–color relations. In order to subtract contributions of fluctuations due to young stellar populations, we use five different g-band magnitude masking thresholds, M g,thres = −3.5, −4.0, −4.5, −5.0, and −5.5 mag. We find that the rms scatter of the linear fit to the relation is the smallest (rms = 0.16 mag) in the case of M g,thres = −4.0 mag, M ¯ i = (−2.65 ± 0.13) + (1.28 ± 0.24) × (g − i)0. This scatter is much smaller than those in the previous studies (rms = 0.26 mag), and is closer to the value for bright red galaxies (rms = 0.12 mag). This calibration is consistent with predictions from metal-poor simple stellar population models.

Effect of Cosmic Mean Metallicity on the Supernovae Cosmology

The initial metallicity of Type Ia Supernovae (SNe Ia) progenitor that is increasing with the cosmological chemical evolution will directly lead to a decrease of the 56Ni formed during the nucleosynthesis and then a varying standard candle. The variation may seriously affect our understanding of the evolving universe. In this work, we derived the relationships between 56Ni yield and metallicity in different progenitor channels. The evolution of the cosmic mean metallicity (CMM) was used to estimate the initial metallicity of progenitors. The effect of the delay times from the birth of progenitors to their explosion was also considered. The corrections of SNe Ia luminosity were estimated and the influences of the different progenitor channels and CMM evolution rates were examined. Several important cosmological parameters were updated according to the luminosity corrections.

Shouldn’t Doppler 'De-boosting' be accounted for in calculations of intrinsic luminosity of Standard Candles?

"Doppler boosting / de-boosting" is a well-known relativistic effect that alters the apparent luminosity of approaching/receding radiation sources. "Doppler boosting" alters the apparent luminosity of approaching light sources to appear brighter, while "Doppler de-boosting" alters the apparent luminosity of receding light sources to appear fainter. While "Doppler boosting / de-boosting" has been successfully accounted for and observed in relativistic jets of AGN, double white dwarfs, in search of exoplanets and stars in binary systems it was ignored in the establishment of Standard Candles for cosmological distances. A Standard Candle adjustment appears necessary for "Doppler de-boosting" for high Z, otherwise we would incorrectly assume that Standard Candles appear dimmer, not because of "Doppler de-boosting" but because of the excessive distance, which would affect the entire Standard Candles ladder at cosmological distances. The ratio between apparent (L) and intrinsic (Lo) luminosities as a function of redshift Z and spectral index α is given by the formula ℳ(Z) = L/Lo=(Z+1)^(α-3) and for Type Ia supernova as ℳ(Z) = L/Lo=(Z+1)^(-2). These formulas are obtained within the framework of Special Relativity and may require adjustments within the General Relativity framework.

"Doppler De-boosting" and the Observation of "Standard Candles" in Cosmology

“Doppler boosting” is a well-known relativistic effect that alters the apparent luminosity of approaching radiation sources. “Doppler de-boosting” is the same relativistic effect observed but for receding light sources (e.g. relativistic jets of AGN and GRB). “Doppler boosting” alters the apparent luminosity of approaching light sources to appear brighter, while “Doppler de-boosting” alters the apparent luminosity of receding light sources to appear fainter. While “Doppler de-boosting” has been successfully accounted for and observed in relativistic jets of AGN, it was ignored in the establishment of Standard candles for cosmological distances. A Standard Candle adjustment of Z>0.1 is necessary for “Doppler de-boosting”, otherwise we would incorrectly assume that Standard Candles appear dimmer, not because of “Doppler de-boosting” but because of the excessive distance, which would affect the entire Standard Candles ladder at cosmological distances. The ratio between apparent (L) and intrinsic (Lo) luminosities as a function of the redshift Z and spectral index α is given by the formula ℳ(Z) = L/Lo=(Z+1)α -3 and for Type Ia supernova appears as ℳ(Z) = L/Lo=(Z+1)-2. “Doppler de-boosting” may also explain the anomalously low luminosity of objects with a high Z without the introduction of an accelerated expansion of the Universe and Dark Energy.

PREPRINT. “Doppler de-boosting” and the observation of “Standard candles” in cosmology.

PREPRINT. “Doppler boosting” is a well-known relativistic effect that alters the apparent luminosity of approaching radiation sources. “Doppler de-boosting” is the term of the same relativistic effect observed for receding light sources (e.g.relativistic jets of active galactic nuclei and gamma-ray bursts). “Doppler boosting” alters the apparent luminosity of approaching light sources to appear brighter, while “Doppler de-boosting” alters the apparent luminosity of receding light sources to appear fainter. While “Doppler de-boosting” has been successfully accounted for and observed in relativistic jets of AGN, it was ignored in the establishment of Standard candles for cosmological distances. A Standard candle adjustment of Z>0.1 is necessary for “Doppler de-boosting”, otherwise we would incorrectly assume that Standard Candles appear dimmer, not because of “Doppler de-boosting” but because of the excessive distance, which would affect the entire Standard Candles ladder at cosmological distances. The ratio between apparent (L) and intrinsic (Lo) luminosities as a function of the redshift Z and spectral index α is given by the formula ℳ(Z) =L/Lo=(Z+1)^(α-3) and for Type Ia supernova appears as ℳ(Z)=L/Lo=(Z+1)^(-2). “Doppler de-boosting” may also explain the anomalously low luminosity of objects with a high Z without the introduction of an accelerated expansion of the Universe and Dark Energy.

Measuring the Hubble function with standard candle clustering

Supernova Ia magnitude surveys measure the dimensionless luminosity distance H0DL. However, from the distances alone one cannot obtain quantities like H(z) or the dark energy equation of state, unless further cosmological assumptions are imposed. Here we show that by measuring the power spectrum of density contrast and of peculiar velocities of supernovae one can estimate also H(z)/H0 regardless of background or linearly perturbed cosmology and of galaxy-matter bias. This method, dubbed Clustering of Standard Candles (CSC) also yields the redshift distortion parameter β(k, z) and the biased matter power spectrum in a model-independent way. We forecast that an optimistic (pessimistic) LSST may be able to constrain H(z)/H0 to 5–13% (9–40%) in redshift bins of Δz = 0.1 up to at least z = 0.6.