Dwarf galaxies are key objects for small-scale cosmological tests like the abundance problems or the planes-of-satellites problem. It is therefore a crucial task to get accurate information for as many nearby dwarf galaxies as possible. Using extremely deep, ground-based $V$ and $i$-band Subaru Suprime Cam photometry with a completeness of $i=27$ mag, we measure the tip of the red giant branch distance for the dwarf galaxy [TT2009] 25. This dwarf resides in the field around the Milky Way-analog NGC 891. By using a Bayesian approach, we measure a distance of $10.28^{+1.17}_{-1.73}$ Mpc, which is consistent with the distance of NGC 891, thus we confirm it as a member of NGC 891. The dwarf galaxy follows the scaling relations defined by the Local Group dwarfs. We do not find an extended stellar halo around [TT2009] 25. In the small field of view of 100 kpc covered by the survey, only one bright dwarf galaxy and the giant stream are apparent. This is comparable to the Milky Way, where one bright dwarfs reside in the same volume, as well as the Sagittarius stream - excluding satellites which are farther away but would be projected in the line-of-sight. It is thus imperative to survey for additional dwarf galaxies in a larger area around NGC 891 to test the abundance of dwarf galaxies and compare it to the number of satellites around the Milky Way.
The primary goal of the Carnegie Chicago Hubble Program (CCHP) is to calibrate the zero-point of the Type Ia supernova (SN Ia) Hubble Diagram through the use of Population II standard candles. So far, the CCHP has measured direct distances to 11 SNe Ia, and here we increase that number to 15 with two new TRGB distances measured to NGC 5643 and NGC 1404, for a total of 20 SN Ia calibrators. We present resolved, point-source photometry from new Hubble Space Telescope (HST) imaging of these two galaxies in the F814W and F606W bandpasses. From each galaxy's stellar halo, we construct an F814W-band…
Previous studies have shown that the large, diffuse galaxies NGC1052-DF2 and NGC1052-DF4 both have populations of unusually luminous globular clusters as well as a very low dark matter content. Here we present newly-obtained deep Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging of one of these galaxies, NGC1052-DF4. We use these data to measure the distance of the galaxy from the location of the tip of the red giant branch (TRGB). We find a rapid increase in the number of detected stars fainter than $m_{F814W} \sim 27.3$, which we identify as the onset of the red giant br…
Archival HST data taken in F606W+F814W of two different fields in the outer regions of NGC 6946 is used to measure a tip of the red giant branch (TRGB) distance to the galaxy. We employ a Bayesian maximum-likelihood modeling method that incorporates the completeness of the photometry, and allows us to model the luminosity function of the RGB population. Our two fields provide us with distances of 7.74 $\pm$ 0.42 Mpc and 7.69 $\pm$ 0.50 Mpc, respectively. Our final distance of 7.72 $\pm$ 0.32 Mpc is higher than most values published previously in the literature. This has important implications …
The large and diffuse galaxies NGC1052-DF2 and NGC1052-DF4 have been found to have very low dark matter content and a population of luminous globular clusters. Accurate distance measurements are key to interpreting these observations. Recently, the distance to NGC1052-DF4 was found to be $20.0\pm 1.6$ Mpc by identifying the tip of the red giant branch (TRGB) in 12 orbits of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging. Here we present 40 orbits of HST ACS data for NGC1052-DF2 and use these data to measure its TRGB. The TRGB is readily apparent in the color-magnitude d…
We present the tip of the red giant branch (TRGB) distances to Type Ia supernova (SNe Ia) host galaxies NGC 4038/39 and NGC 5584. Based on the deep images constructed using archival Hubble Space Telescope data, we detect red giant branch stars in each galaxy. VI photometry of the resolved stars and corresponding I-band luminosity functions show the TRGB to be at I_{TRGB} = 27.67 \pm 0.05 for NGC 4038/39 and I_{TRGB} = 27.77 \pm 0.04 for NGC 5584. From these estimates, we determine the distance modulus to NGC 4038/39 to be (m-M)_0 = 31.67 \pm 0.05 (random) \pm 0.12 (systematic) (corresponding t…
In the nearby galaxy NGC 4258, the well-modeled orbital motion of H$_2$O masers about its supermassive black hole provides the means to measure a precise geometric distance. As a result, NGC 4258 is one of a few "geometric anchors" available to calibrate the true luminosities of stellar distance indicators such as the Tip of the Red Giant Branch (TRGB) or the Cepheid Leavitt law. In this paper, we present a detailed study of the apparent magnitude of the TRGB within NGC 4258 using publicly-available HST observations optimally situated in the gas- and dust-free halo along the minor axis, spanni…
The Carnegie-Chicago Hubble Program seeks to anchor the distance scale of Type Ia supernovae via the Tip of the Red Giant Branch (TRGB). Based on deep $Hubble$ $Space$ $Telescope$ ACS/WFC imaging, we present an analysis of the TRGB for the metal-poor halo of NGC 1365, a giant spiral galaxy in the Fornax Cluster that is host to the supernova SN2012fr. We have measured its extinction-corrected TRGB magnitude to be F814W $= 27.34 \pm 0.03_{stat} \pm0.01_{sys}$ mag. In advance of future direct calibration by $Gaia$, we set a provisional TRGB luminosity via the Large Magellanic Cloud and find a tru…
The Carnegie-Chicago Hubble Program (CCHP) is undertaking a re-calibration of the extragalactic distance scale, using Type Ia supernovae that are tied to Tip of the Red Giant Branch (TRGB) distances to local galaxies. We present here deep Hubble Space Telescope (HST) ACS/WFC imaging of the resolved stellar populations in the metal-poor halos of the SN Ia host galaxies NGC 4424, NGC 4526, and NGC 4536. These three Virgo constellation galaxies are prime targets for calibrating the extragalactic distance scale given their relative proximity in the local Universe and their low line-of-sight redden…
The Carnegie-Chicago Hubble Program (CCHP) is re-calibrating the extragalactic SN Ia distance scale using exclusively Population II stars. This effort focuses on the Tip of the Red Giant Branch (TRGB) method, whose systematics are entirely independent of the Population I Cepheid-based determinations that have long served as calibrators for the SN Ia distance scale. We present deep Hubble Space Telescope imaging of the low surface-density and low line-of-sight reddening halos of two galaxies, NGC 1448 and NGC 1316, each of which have been hosts to recent SN Ia events. Provisionally anchoring th…
The tip of the red giant branch is one of the widely used distance measurement methods for the relatively nearby galaxies where the bright individual stars are resolved. Most of the earlier works have used the Photometry in the I-band such as HST ACS/WFC F814W or F850LP for the RGB tip method. Here we look into the RGB tip magnitudes in J-band such as HST WFC3/IR F110W and JWST NIRCam/WF F115W for a wide range of age and metallicity. We find that the J-band (HST WFC3/IR F110W and JWST NIRCam/WF F115W) RGB tip magnitudes do not significantly change compared to that of the I-band (HST ACS/WFC F8…
We present final results of a program for the determination of the Hubble constant based on the calibration of the Type Ia supernovae (SNe Ia) using the Tip of the Red Giant Branch (TRGB). We report TRGB distances to three SN Ia host galaxies, NGC 3021, NGC 3370, and NGC 1309. We obtain F555W and F814W photometry of resolved stars from the archival Hubble Space Telescope data. Luminosity functions of red giant stars in the outer regions of these galaxies show the TRGB to be at I ~ QT = 28.2 ~ 28.5 mag. From these TRGB magnitudes and the revised TRGB calibration based on two distance anchors (N…
Indications from Gaia data release 2 (DR2) are that the tip of the red giant branch (TRGB, a population II standard candle related to the helium flash in low mass stars) is close to -4 in absolute I magnitude in the Cousins photometric system. Our sample is high latitude southern stars from the thick disk and inner halo, and our result is consistent with longstanding findings from globular clusters, whose distances were calibrated with RR Lyrae stars. As the Gaia mission proceeds, there is every reason to think an accurate Galactic geometric calibration of TRGB will be a significant outcome.
We present a precise optical and near-infrared determination of the Tip of the Red Giant Branch (TRGB) brightness in the Large and Small Magellanic Clouds (respectively LMC and SMC). The commonly used calibrations of the absolute magnitude of the TRGB lead to an overestimation of the distance to the LMC and SMC in the K band, and an underestimation of the distance in the optical I band for both galaxies. Reported discrepancies are at the level of 0.2 mag, with respect to the very accurate distance determinations to both Clouds based on late-type eclipsing binaries. The differential distances b…
Population II Distance Indicators: RR Lyrae Variables, Tip of the Red Giant Branch (TRGB) Stars and J-Branch Asymptotic Giant Branch (JAGB/Carbon) Stars
We determine the distances to the Type Ia Supernova host galaxies M66 (NGC 3627) and M96 (NGC 3368) of the Leo I Group using the Tip of the Red Giant Branch (TRGB) method. We target the stellar halos of these galaxies using the Hubble Space Telescope ACS/WFC in the F606W and F814W bandpasses. By pointing to the stellar halos we sample RGB stars predominantly of Population II, minimize host-galaxy reddening, and significantly reduce the effects of source crowding. Our absolute calibration of the I-band TRGB is based on a recent detached eclipsing binary distance to the Large Magellanic Cloud. W…
We report the presence of two distinct red giant branches (RGBs) in the globular cluster NGC 288 from the narrow-band calcium and Strömgren b & y photometry obtained at the CTIO 4m Blanco telescope. The RGB of NGC 288 is clearly split into two in the hk [=(Ca - b) - (b - y)] index, while the split is not shown in the b - y color. Unlike other globular clusters with multiple populations reported thus far, the horizontal branch of NGC 288 is only mildly extended. Our stellar population models show that this and the presence of two distinct RGBs in NGC 288 can be reproduced if slightly metal-rich…
The Extragalactic Distance Database (EDD) was created as a repository for high quality, redshift-independent distances. A key component of EDD is the Color Magnitude Diagrams/Tip of the Red Giant Branch (CMDs/TRGB) catalog, which provides information on the stellar content of nearby galaxies observed with the Hubble Space Telescope (HST). Here we provide a decadal update to this catalog, which has now doubled in size to over 500 galaxies. We highlight the additions to our data reduction and analysis techniques, and provide examples of the science that has been made possible with this large dat…
In this paper, we extend the use of the tip of the red giant branch (TRGB) method to near-infrared wavelengths from previously-used $I$-band, using the \textit{Hubble Space Telescope (HST)} Wide Field Camera 3 (WFC3). Upon calibration of a color dependency of the TRGB magnitude, the IR TRGB yields a random uncertainty of $\sim 5%$ in relative distance. The IR TRGB methodology has an advantage over the previously-used ACS $F606W$ and $F814W$ filter set for galaxies that suffer from severe extinction. Using the IR TRGB methodology, we obtain distances toward three principal galaxies in the Maffe…
M74 (NGC 628) is a famous face-on spiral galaxy, hosting three core-collapse supernovae (SNe):SN Ic 2002ap, SN II-P 2003gd, and SN II-P 2013ej. However its distance is not well known. We present a distance estimation for this galaxy based on the Tip of the Red Giant Branch (TRGB) method. We obtain photometry of the resolved stars in the arm-free region of M74 from F555W and F814W images in the Hubble Space Telescope archive. The color-magnitude diagram of the resolved stars shows a dominant red giant branch (RGB) as well as blue main sequence stars, red helium burning stars, and asymptotic gia…
In this paper we review the various high precision methods that are now available to determine the distance to NGC 5128. These methods include: Cepheids, TRGB (tip of the red giant branch), PNLF (planetary nebula luminosity function), SBF (surface brightness fluctuations) and Long Period Variable (LPV) Mira stars. From an evaluation of these methods and their uncertainties, we derive a best-estimate distance of 3.8 +- 0.1 Mpc to NGC 5128 and find that this mean is now well supported by the current data. We also discuss the role of NGC 5128 more generally for the extragalactic distance scale as…
NGC 6441 is one of the most massive and most metal-rich globular clusters in the galaxy, and is noted for an unusual extended horizontal branch which reaches past the instability strip. We find evidence that there are two different populations of stars within the heavily-populated red clump. Once a differential reddening correction is applied, a large but compact group of stars is found at the faint red end of the clump in the color magnitude diagram. Brighter, bluer stars in the clump are found to be more centrally concentrated within the cluster at very high level of significance. Curiously,…
There is a growing body of evidence for the presence of multiple stellar populations in some globular clusters, including NGC 1851. For most of these peculiar globular clusters, however, the evidence for the multiple red giant-branches (RGBs) having different heavy elemental abundances as observed in Omega Centauri is hitherto lacking, although spreads in some lighter elements are reported. It is therefore not clear whether they also share the suggested dwarf galaxy origin of Omega Cen or not. Here we show from the CTIO 4m UVI photometry of the globular cluster NGC 1851 that its RGB is clearly…
The red giant branch tip in the SDSS, PS1, JWST, NGRST and Euclid photometric systems. Calibration in optical passbands using Gaia DR3 synthetic photometry
We present a revised TRGB calibration, accurate to 2.7% of distance. A modified TRGB magnitude corrected for the color dependence of the TRGB, the QT magnitude, is introduced for better measurement of the TRGB. We determine the color-magnitude relation of the TRGB from photometry of deep images of HST/ACS fields around eight nearby galaxies. The zero-point of the TRGB at the fiducial metallicity ([Fe/H]=-1.6 ((V-I)_{0,TRGB}=1.5)) is obtained from photometry of two distance anchors, NGC 4258 (M106) and the LMC, to which precise geometric distances are known: M_{QT,TRGB}=-4.023+-0.073 mag from N…
The Carnegie-Chicago Hubble Program (CCHP) is building a direct path to the Hubble constant (H0) using Population II stars as the calibrator of the SN Ia-based distance scale. This path to calibrate the SN Ia is independent of the systematics in the traditional Cepheid-based technique. In this paper, we present the distance to M101, the host to SN2011fe, using the I-band tip of the red giant branch (TRGB) based on observations from the ACS/WFC instrument on the Hubble Space Telescope. The CCHP targets the halo of M101 where there is little to no host-galaxy dust, the red giant branch is isolat…
Accurate distances are fundamental to interpreting many measured properties of galaxies. Surprisingly, many of the best-studied spiral galaxies in the Local Volume have distance uncertainties that are much larger than can be achieved with modern observations. Using Hubble Space Telescope optical imaging, we use the tip of the red giant branch method to measure the distances to six galaxies that are included in the Spitzer Infrared Nearby Galaxies Survey (SINGS) program and its offspring surveys. The sample includes M63, M74, NGC 1291, NGC 4559, NGC 4625, and NGC 5398. We compare our results wi…
PHANGS-HST is an ultraviolet-optical imaging survey of 38 spiral galaxies within ~20 Mpc. Combined with the PHANGS-ALMA, PHANGS-MUSE surveys and other multiwavelength data, the dataset will provide an unprecedented look into the connections between young stars, HII regions, and cold molecular gas in these nearby star-forming galaxies. Accurate distances are needed to transform measured observables into physical parameters (e.g., brightness to luminosity, angular to physical sizes of molecular clouds, star clusters and associations). PHANGS-HST has obtained parallel ACS imaging of the galaxy ha…
Using multi-epoch JHK photometry obtained with the 1.4-m Japanese-South African Infrared Survey Facility at Sutherland we have identified large numbers of AGB variables in NGC 6822. This paper uses 30 large amplitude variables, with periods ranging from about 200 to 900 days, to provide a new calibration of the period-luminosity relation.
We present radial velocities and chemical abundances for red giant branch stars in the Galactic bulge globular clusters NGC 6342 and NGC 6366. The velocities and abundances are based on measurements of high resolution (R > 20,000) spectra obtained with the MMT-Hectochelle and WIYN-Hydra spectrographs. We find that NGC 6342 has a heliocentric radial velocity of +112.5 km/s (sigma = 8.6 km/s), NGC 6366 has a heliocentric radial velocity of -122.3 km/s (sigma = 1.5 km/s), and that both clusters have nearly identical metallicities ([Fe/H] ~ -0.55). NGC 6366 shows evidence of a moderately extended …
Astrophysical Distance Scale VII: A Self-Consistent, Multi-Wavelength Calibration of the Slopes and Relative Zero Points for the Run of Luminosity with Color of Stars Defining the Tip of the Red Giant Branch
We present a new method to measure colors and magnitudes of the tip of the red giant branch in multiple bandpasses simultaneously by fitting an n-dimensional Gaussian to photometry of candidate tip stars. We demonstrate that this method has several advantages over traditional edge detection, particularly in regimes where the TRGB magnitude is strongly color-dependent, as is the case in the near-infrared. We apply this method to a re-reduction of a set of optical and near-IR HST data originally presented in Dalcanton et al. (2012). The re-reduction takes advantage of the increased depth and acc…
The tip of the red giant branch has been used to measure distances to 500 nearby galaxies with the Hubble Space Telescope (HST) which are available in the Color-Magnitude Diagrams and Tip of the Red Giant Branch (CMDs/TRGB) catalog on the Extragalactic Distance Database (EDD). Our established methods are employed to perform an independent reduction of the targets presented by the Carnegie-Chicago Hubble Program (CCHP) in the series of papers culminating in Freedman (2021). Our distinct methodology involves modeling the observed luminosity function of red giant branch and asymptotic giant branc…
Multiple stellar populations (MPs) representing star-to-star light-element abundance variations are common in nearly all ancient Galactic globular clusters. Here we provide the strongest evidence yet that the populous, ~ 1.7 Gyr-old Large Magellanic Cloud cluster NGC 2173 also exhibits light-element abundance variations. Thus, our results suggest that NGC 2173 is the youngest cluster for which MPs have been confirmed to date. Our conclusion is based on the distinct bifurcation at the tip of its red-giant branch in high-quality color--magnitude diagrams generated from Hubble Space Telescope ima…
Using high precision ground-based photometry for 46 low-reddening Galactic globular clusters, in conjunction with Gaia DR2 proper motions for member star selection, we have calibrated the zero point of the tip of the red giant branch (TRGB) method at two optical ($VI$) and three near-infrared ($JHK$) wavelengths. In doing so, we utilized the sharply-defined zero-age horizontal branch (ZAHB) of these clusters to relatively calibrate our cluster sample into a composite color-magnitude diagram spanning a wide range of metallicities, before setting the absolute zero point of this composite using t…
We derived chemical abundances for C, N, O, Na, Mg and Al in 20 asymptotic giant branch (AGB) stars in the globular cluster NGC 6752. All these elements (but Mg) show intrinsic star-to-star variations and statistically significant correlations or anticorrelations analogous to those commonly observed in red giant stars of globular clusters hosting multiple populations. This demonstrates that, at odds with previous findings, both first and second generation stars populate the AGB of NGC 6752. The comparison with the Na abundances of red giant branch stars in the same cluster reveals that second …
We use data from the ESA Gaia mission Early Data Release 3 (EDR3) to measure the trigonometric parallax of $ω$ Cen, the first high precision parallax measurement for the most massive globular cluster in the Milky Way. We use a combination of positional and high quality proper motion data from EDR3 to identify over 100,000 cluster members, of which 67,000 are in the magnitude and color range where EDR3 parallaxes are best calibrated. We find the estimated parallax to be robust, demonstrating good control of systematics within the color-magnitude diagram of the cluster. We find a parallax for th…
We obtained FLAMES GIRAFFE+UVES spectra for both first and second-generation red giant branch (RGB) stars in the globular cluster (GC) NGC 362 and used them to derive abundances of 21 atomic species for a sample of 92 stars. The surveyed elements include proton-capture (O, Na, Mg, Al, Si), alpha-capture (Ca, Ti), Fe-peak (Sc, V, Mn, Co, Ni, Cu), and neutron-capture elements (Y, Zr, Ba, La, Ce, Nd, Eu, Dy). The analysis is fully consistent with that presented for twenty GCs in previous papers of this series. Stars in NGC 362 seem to be clustered into two discrete groups along the Na-O anti-corr…
We obtain high resolution spectra of nine red giant branch stars in NGC 6681 and perform the first detailed abundance analysis of stars in this cluster. We confirm cluster membership for these stars based on consistent radial velocities of 214.5$\pm$3.7 km/s and find a mean [Fe/H] = -1.63$\pm$0.07 dex and [α/Fe] = 0.42$\pm$0.11 dex. Additionally, we confirm the existence of a Na-O anti-correlation in NGC 6681 and identify two populations of stars with unique abundance trends. With the use of HST photometry from Sarajedini et al. (2007) and Piotto et al. (2015) we are able to identify these two…
We exploit multi-band Hubble Space Telescope photometry to investigate multiple populations (MPs) along the red horizontal branches (HBs) and red clumps of fourteen metal-rich Globular Clusters (GCs), including twelve Milky Way GCs and the Magellanic Cloud GCs NGC 1978 and NGC 416. Based on appropriate two-color diagrams we find that the fraction of 1G stars in Galactic GCs correlates with cluster mass, confirming previous results based on red-giant branch (RGB) stars. Magellanic-Cloud GCs show higher fractions of 1G stars than Galactic GCs with similar masses, thus suggesting that the environ…
We present a new empirical \(JHK\) absolute calibration of the tip of the red giant branch (TRGB) in the Large Magellanic Cloud (LMC). We use published data from the extensive \emph{Near-Infrared Synoptic Survey} containing 3.5 million stars, of which 65,000 are red giants that fall within one magnitude of the TRGB. Adopting the TRGB slopes from a companion study of the isolated dwarf galaxy IC\,1613 as well as an LMC distance modulus of \(μ_0 = \)~18.49~mag from (geometric) detached eclipsing binaries, we derive absolute \(JHK\) zero-points for the near-infrared TRGB. For comparison with meas…
NGC 6388 and NGC 6441 are two massive Galactic bulge globular clusters which share many properties, including the presence of an extended horizontal branch (HB), quite unexpected because of their high metal content. In this paper we use HST's WFPC2, ACS, and WFC3 images and present a broad multicolor study of their stellar content, covering all main evolutionary branches. The color-magnitude diagrams (CMDs) give compelling evidence that both clusters host at least two stellar populations, which manifest themselves in different ways. NGC 6388 has a broadened main sequence (MS), a split sub-gian…
Understanding the exact extent and content of tidal tails of open clusters provide useful clues on how field stars populate the Milky Way. We reanalyse, using Gaia EDR3 data, the tails around the open cluster NGC 752. Compared to previous analyses, we look at a much wider region around the cluster and use first the convergent point method, coupled with a clustering analysis using DBSCAN. We find that the cluster, located 433 pc away and well described by a Plummer profile, has very long and asymmetric tails, extending more than 260 pc on the sky (from tip to tip) - four times larger than previ…
A second galaxy ``missing dark matter" (NGC1052-DF4) has been recently reported. Here we show, using the location of the Tip of the Red Giant Branch (TRGB), that the distance to this galaxy is 14.2+-0.7 Mpc. This locates the galaxy 6 Mpc closer than previously determined. We also analyse the distances to the brightest galaxies in the field-of-view (FOV) of NGC1052. We find this field is populated by two groups of galaxies in projection: one dominated by NGC1052 and NGC1047 at ~19 Mpc and another group containing NGC1042 and NGC1035 (as well as [KKS2000]04 and NGC1052-DF4) at ~13.5 Mpc. At a di…
It has recently been suggested that the presence of multiple populations showing various amounts of helium enhancement is the rule, rather than the exception, among globular star clusters. An important prediction of this helium enhancement scenario is that the helium-enhanced blue horizontal branch (HB) stars should be brighter than the red HB stars which are not helium-enhanced. In this Letter, we test this prediction in the case of the Galactic globular cluster M3 (NGC 5272), for which the helium-enhancement scenario predicts helium enhancements of > 0.02 in virtually all blue HB stars. Usin…
Based on observations from the \emph{FourStar} near-infrared camera on the 6.5m Baade-Magellan telescope at Las Campanas, Chile, we present calibrations of the $JHK$ luminosities of stars defining the tip of the red giant branch (TRGB) in the halo of the Local Group dwarf galaxy IC 1613. We employ metallicity-independent (rectified) T-band magnitudes---constructed using $J,H$ and $K$-band magnitudes and both $(J-H)~ \& ~(J-K)$ colors in order to flatten the upward-sloping red giant branch tips as otherwise seen in their apparent color-magnitude diagrams. We describe and quantify the advantages…
We present the first measure of Fe and Na abundances in NGC 6362, a low-mass globular cluster where first and second generation stars are fully spatially mixed. A total of 160 member stars (along the red giant branch and the red horizontal branch) have been observed with the multi-object spectrograph FLAMES at the Very Large Telescope. We find that the cluster has an iron abundance of [Fe/H]=--1.09$\pm$0.01 dex, without evidence of intrinsic dispersion. On the other hand, the [Na/Fe] distribution turns out to be intrinsically broad and bimodal. The Na-poor and Na-rich stars populate, respectiv…
IC 1613 is an isolated dwarf galaxy within the Local Group. Low foreground and internal extinction, low metallicity, and low crowding make it an invaluable testbed for the calibration of the local distance ladder. We present new, high-fidelity distance estimates to IC 1613 via its Tip of the Red Giant Branch (TRGB) and its RR Lyrae (RRL) variables as part of the Carnegie-Chicago Hubble Program, which seeks an alternate local route to \ho using Population II stars. We have measured a TRGB magnitude I=20.35+/-0.01 (statistical)+/-0.01 (systematic) using wide-field observations obtained from the …
The calibration of the tip of the red giant branch (TRGB) in the $I$-band has a direct role in determinations of the Hubble constant, a subject of recent interest due to the discrepancy between direct and indirect estimates of its value. We present a maximum likelihood (ML) method designed to obtain an independent calibration of the brightness of TRGB using $Gaia$ parallaxes from the Early Data Release 3 (EDR3) of Milky Way field Giants at high Galactic latitude. We adopt simple parameterizations for the Milky Way stellar luminosity function and density law and and optimize the likelihood of t…
JHKs photometry is presented from a 3.5 year survey of the central regions of the irregular galaxy NGC6822. The morphology of the colour-magnitude and colour-colour diagrams is discussed with particular reference to M, S and C-type AGB stars and to M-supergiants. Mean JHKs magnitudes and periods are given for 11 O-rich and 50 presumed C-rich Miras. Data are also listed for 27 large amplitude AGB stars without periods and for 69 small amplitude AGB variables. The slope of the bolometric period-luminosity relation for the C-rich Miras is in good agreement with that in the LMC. Distance moduli de…
The brightness of the tip of the red-giant branch (TRGB) allows one to constrain novel energy losses that would lead to a larger core mass at helium ignition and thus to a brighter TRGB than expected by standard stellar models. The required absolute TRGB calibrations strongly improve with reliable geometric distances that have become available for the galaxy NGC 4258 that hosts a water megamaser and to the Large Magellanic Cloud based on 20 detached eclipsing binaries. Moreover, we revise a previous TRGB calibration in the globular cluster $ω$ Centauri with a recent kinematical distance determ…
Photometric and spectroscopic analyses have shown that the Galactic bulge cluster Terzan 5 hosts several populations with different metallicities and ages that manifest as a double red horizontal branch (HB). A recent investigation of the massive bulge cluster NGC 6569 revealed a similar, though less extended, HB luminosity split, but little is known about the cluster's detailed chemical composition. Therefore, we have used high-resolution spectra from the Magellan-M2FS and VLT-FLAMES spectrographs to investigate the chemical compositions and radial velocity distributions of red giant branch a…
