arXiv subjects

Allan Sandage

Publications and source records attributed to Allan Sandage.

At least 19 recordsLinked to original sources

arXiv2015

Comparison of Hipparcos Trigonometric and Mount Wilson Spectroscopic Parallaxes for 90 Subgiants that Defined the Class in 1935

A history is given of the discovery between 1914 and 1935 of stars of intermediate luminosity between giants and dwarfs with spectral types between G0 to K3. The Mt Wilson spectroscopists identified about 90 such stars in their 1935 summary paper of spectroscopic absolute magnitudes for 4179 stars. Called "subgiants" by Strömberg, these 90 stars defined the group at the time. The position of the Mt Wilson subgiants in the HR diagram caused difficulties in comparisons of high weight trigonometric parallaxes being measured and with Russell's prevailing evolution proposal, and critics questioned the reality of the Mt Wilson subgiants. We compare, star-by-star, the Mt Wilson spectroscopic absolute magnitudes of the 90 stars defining their sample against those absolute magnitudes derived from Hipparcos (HIP) trigonometric parallaxes. We address concerns over biases in the Mt Wilson calibration sample and biases created by the adopted methodology for calibration. Historically, these concerns were sufficient to discredit the discovery of subgiants in the Mt Wilson sample. However, as shown here, the majority of the Mount Wilson stars identified as subgiants that also have reliable HIP trigonometric parallaxes do lie among the subgiant sequence in the HIP HR diagram. Moreover, no significant offset is seen between the M(V) brightnesses derived from the Mt Wilson spectroscopic parallaxes and the M(V) values derived from Hipparcos trigonometric parallaxes with a fractional error of 10%, which confirms in an impressive manner the efficacy of the original Mt Wilson assessments. The existence of subgiants proved that Russell's contraction proposal for stellar evolution from giants to the main sequence was incorrect. Instead, Gamow's 1944 unpublished conjecture that subgiants are post main-sequence stars just having left the main sequence was very nearly correct but was a decade before its time.

astro-ph.GA↗

arXiv2010

Amplitude Fine-Structure in the Cepheid P-L Relation I: Amplitude Distribution Across the RR Lyrae Instability Strip Mapped Using the Accessibility Restriction Imposed by the Horizontal Branch

The largest amplitude light curves for both RR Lyrae (RRL) variables and classical Cepheids with periods less than 10 days and greater than 20 days occur at the blue edge of the respective instability strips. It is shown that the equation for the decrease in amplitude with penetration into the strip from the blue edge, and hence the amplitude fine structure within the strip, is the same for RRL and the Cepheids despite their metallicity differences. However, the manifestation of this identity is different between the two classes of variables because the sampling of the RRL strip is restricted by the discrete strip positions of the horizontal branch, a restriction that is absent for the Cepheids in stellar aggregates with a variety of ages. To show the similarity of the strip amplitude fine structure for RRL and Cepheids we make a grid of lines of constant amplitude in the HR diagram of the strip using amplitude data for classical Cepheids in the Galaxy, LMC, and SMC. The model implicit in the grid, that also contains lines of constant period, is used to predict the correlations between period, amplitude, and color for the two Oosterhoff RRL groups in globular clusters. The good agreement of the predictions with the observations using the classical Cepheid amplitude fine structure also for the RRL shows one aspect of the unity of the pulsation processes between the two classes of variables.

astro-ph.GA↗

arXiv2009

The Tolman Surface Brightness Test for the Reality of the Expansion. V. Provenance of the Test and a New Representation of the Data for Three Remote HST Galaxy Clusters

A new reduction is made of the HST photometric data for E galaxies in three remote clusters at redshifts near z=0.85 in search for the Tolman surface brightness (SB) signal for the reality of the expansion. Because of the strong variation of SB of such galaxies with intrinsic size, and because the Tolman test is about surface brightness, we must account for the variation. In an earlier version of the test, Lubin & Sandage calibrated the variation out. In contrast, the test is made here using fixed radius bins for both the local and remote samples. Homologous positions in the galaxy image at which to compare the surface brightness values are defined by radii at five Petrosian eta values ranging from 1.0 to 2.0. Sersic luminosity profiles are used to generate two diagnostic diagrams that define the mean SB distribution across the galaxy image. A Sersic exponent, defined by the r^n family of Sersic profiles, of n=0.46 fits both the local and remote samples. Diagrams of the dimming of the with redshift over the range of Petrosian eta radii shows a highly significance Tolman signal but degraded by luminosity evolution in the look-back time. The expansion is real and a luminosity evolution exists at the mean redshift of the HST clusters of 0.8 mag in R_cape and 0.4 mag in the I_cape photometric rest-frame bands, consistent with the evolution models of Bruzual and Charlot.

astro-ph.CO↗

arXiv2008

Temperature Differences in the Cepheid Instability Strip Require Differences in the Period-Luminosity Relation in Slope and Zero Point

A graphical and an algebraic demonstration is made to show why the slope and zero point of the Cepheid period-luminosity (P-L) relation is rigidly coupled with the slope and zero point of the Cepheid instability strip in the HR diagram. The graphical demonstration uses an arbitrary (toy) ridge line in the instability strip, while the algebraic demonstration uses the pulsation equation into which the observed P-L relations for the Galaxy and the LMC are put to predict the temperature zero points and slopes of the instability strips. Agreement between the predicted and measured instability strip slopes argue that the observed P-L differences between the Galaxy and LMC are real. In another proof, the direct evidence for different P-L slopes in different galaxies is shown by comparing the Cepheid data in the Galaxy, the combined data in NGC 3351 and NGC 4321, in M31, LMC, SMC, IC 1613, NGC 3109, and in Sextans A+B. The P-L slopes for the Galaxy, NGC 3351, NGC 4321, and M31 are nearly identical and are the steepest in the sample. The P-L slopes decrease monotonically with metallicity in the order listed, showing that the P-L relation is not the same in different galaxies, complicating their use in calibrating the extragalactic distance scale.

astro-ph↗

arXiv2007

Bias Properties of Extragalactic Distance Indicators XII: Bias Effects of Slope Differences and Intrinsic Dispersion on Tully-Fisher Distances to Galaxy Clusters with Application to the Virgo Cluster

The Teerikorpi incompleteness bias in the distance modulus of a galaxy cluster that is determined from incomplete data using the Tully-Fisher (TF) method is discussed differently than has been done in earlier papers of this series. A toy cluster is made with zero intrinsic TF dispersion but with slopes that differ between the calibrators and the cluster data, showing the bias caused by incorrect slopes. Intrinsic dispersion is added to the model and two strategies are used to analyze the data; first by binning the data by line width and then by apparent magnitude (the direct method), and second by binning by magnitude and then summing over all line widths (the inverse method). To illustrate these strategies, a composite cluster is made by combining the observations of Virgo A and B subclusters with those for the Ursa Major I and II clusters, corrected to the Virgo A distance. The cluster data are calibrated using Cepheid distances to 25 galaxies that have adequate TF properties. Different moduli calculated with varying completeness limits are displayed. The cluster modulus derived from the complete cluster sample gives (m-M) = 31.42 +/- 0.2 (external) for Virgo A, 31.80 +/- 0.16 for Virgo B, 31.26 +/- 0.13 for UMa I, and 31.58 +/- 0.17 for UMa II. Combining the Virgo A distance (D = 19.2 Mpc that has a range from 17.5 to 21.1 Mpc with its expansion velocity of 1175 +/- 50 km/s as tied to the remote kinematic frame gives a Hubble constant of 61km/s/Mpc with a range from 53 to 70.

astro-ph↗

arXiv2006

The Distance to the Virgo Cluster from a Recalibrated Tully-Fisher Relation Based on HST Cepheids and a Demonstrated Teerikorpi Cluster Incompleteness Bias

The importance of the distance of the Virgo cluster in the ongoing debate on the value of the Hubble constant is reviewed. A new calibration of the Tully-Fisher 21-cm line width-absolute magnitude relation is made using Cepheid distances to 25 galaxies determined in various HST programs and reduced with the new Cepheid P-L relations that vary from galaxy-to galaxy. The calibration is applied to a complete sample of Virgo cluster spirals for the purpose of demonstrating the Teerikorpi cluster incompleteness bias. A diagnostic test is shown that should be useful in identifying the presence of bias in incompletely sampled data for distant clusters. The bias-free TF distance modulus for the Virgo cluster is m - M = 31.67 (D = 21.6 Mpc). A systematic correction of 0.07 mag is made because the cluster members are redder in B I on average than the calibrators at a given line width, giving a final adopted modulus for the Virgo cluster core of 31.60 + 0.09. If we assign a generous range of systematic error of ~ 0.3 mag, the distance D = 20.9 Mpc (m - M = 31.60) has a range from 24.0 Mpc to 18.2 Mpc (m - M between 31.9 and 31.3), and a Hubble constant of Ho = 56 between the limits of 49 and 65 when used with a cosmic expansion velocity of 1175 km s-1 determined by the method of distance ratios of remote clusters to Virgo. This range overlaps our preferred value of Ho = 62 from the HST Cepheid calibration of type Ia supernovae recently determined. The TF modulus of Virgo determined here cannot be reconciled with the recent high value of Ho = 72 from Freedman et al.

astro-ph↗

arXiv2005

On the Predicted and Observed Color Boundaries of the RR Lyrae Instability Strip as a Function of Metallicity

The purpose of the paper is to predict the temperature at the fundamental blue edge (FBE) of the instability strip for RR Lyrae (RRL) variables from the pulsation equation that relates temperature to period, luminosity, and mass. Modern data for the correlations between period, luminosity, and metallicity at the FBE for field and cluster RRL are used for the temperature calculation. The predicted temperatures are changed to B-V colors using an adopted color transformation. The predicted temperatures at the FBE become hotter as [Fe/H] changes from 0 to -1.5, and thereafter cooler as the metallicity decreases to -2.5 and beyond. The temperature range over this interval of metallicity is $Δ$log $T_e$ = 0.04, or 640 K at 6900K. The predicted color variation is at the level of 0.03 mag in B-V. The predictions are compared with the observed RRL colors at the FBE for both the field and cluster variables, showing general agreement at the level of 0.02 mag in (B-V)$_o$, which, however, is the uncertainty of the reddening corrections. The focus of the problem is then reversed by fitting a better envelope to the observed FBE relation between color and metallicity for metallicities smaller than -1.8 which, when inserted in the pulsation equation, gives a non-linear calibration ....

astro-ph↗

arXiv2004

The Metallicity Dependence of the Fourier Components of RR Lyrae Light Curves is the Oosterhoff/Arp/Preston Period Ratio Effect in Disguise

The correlation of particular Fourier components of the light curves of RR Lyrae variables with metallicity, discovered by Simon and later by Kovacs and his coworkers, is shown to have the same explanation as the period ratios (period shifts in log P) between RRab Lyrae variables that have the same colors, amplitudes, and light-curve shapes but different metallicities. A purpose of this paper is to demonstrate that the model which predicts the period-metallicity relations is the mediating parameters of colors, amplitudes, and light-curve shapes also explains the Simon/Kovacs et al. correlation between period, Phi_31, and metallicity. The proof is made by demonstrating that the combination of the first and third phase terms in a Fourier decomposition of RRab light curves, called Phi_31 by Simon and Lee, varies monotonically across the RR Lyrae instability strip in the same way that amplitude, color, and rise time vary with period within the strip. The premise of the model is that if horizontal branches at the RR Lyrae strip are stacked in luminosity according to the metallicity, then there necessarily must be a log period shift between RR Lyraes with different metallicities at the same Phi_31 values. However, there are exceptions to the model. (...)

astro-ph↗

arXiv2004

New Calibrations of Pulsational Absolute Magnitudes of Field RR Lyrae Stars Using Revised Dependencies of Temperatures, Masses, and Periods on Metallicity

The pulsational method to estimate the absolute magnitudes of RR Lyrae stars is updated with new data on field-star metallicities by Layden, a new calibration of the (B-V)_0-temperature correlation from recent atmospheric models by Bell and Tripicco, and new mass estimates by Bono et al. New linear and non-linear calibrations of M_V(RR)=f([Fe/H]) are derived that depend on the nature of the adopted envelope in a diagram of log period versus metallicity fitted to the shortest period field variables in each metallicity range, together with the stated assumptions on the colour of the stars at that envelope. These new cali- brations are compared with a recent non-linear calibration by Caputo et al. The theoretical luminosity zero points for each of the three new calibrations derived here agree with each other to within 0.1 mag over the metallicity range of -1.0>[Fe/H]>-2.0. Comparison with the empirical absolute magnitude calibra- tion of M_V(RR)=+0.52 at [Fe/H]=-1.5 by Clementini at al. from RR Lyraes in LMC also shows agreement at the 0.05 mag level at the stated metallicity. Our final compromise pulsational calibration is, M_V(RR)=0.82 + 0.20([Fe/H]) with the caveat that the true relation is likely to be non-linear at the 0.1 mag level for [Fe/H] values between -0.5 and -2.0, hence with variable dM_V/d([Fe/H]) slopes that cover the range from 0 to 0.6 for different metallicities. (...)

astro-ph↗

arXiv2003

The Cepheid Distance to NGC 5236 (M 83) with the VLT

Cepheids have been observed in NGC 5236 (M 83) using the ANTU (UT1) 8.2 meter telescope of the ESO VLT with FORS1. Observations over 34 epochs in V and I have been made between January 2000 and July 2001. Twelve Cepheid candidates have periods between 12 and 55 days. The true distance modulus is adopted to be (m-M)_0 = 28.25 +/- 0.15, which corresponds to a distance of 4.5 +/- 0.3 Mpc. The distance of NGC 5253 has been rediscussed. The mean distance of (m-M)_0 = 28.01 +/- 0.15 (based on SN 1972E) shows the galaxy to be a close neighbor of M 83 (separation = 0.5 +/- 0.4 Mpc), suggesting that the two galaxies may have interacted in the past and thus possibly explaining the amorphous morphology of NGC 5253. M 83 is the principal member of the nearby M 83 group containing also, besides NGC 5253, several dwarf members, for five of which TRGB distances are available (Karachentsev et al. 2002a, A&A, 385, 21). The adopted group distance of (m-M)_0 = 28.28 +/- 0.10 (4.5 +/- 0.2 Mpc) together with its mean recession velocity of v_LG = 249 +/- 42 km/s shows again the extreme quietness of the local (1 Mpc to 10 Mpc) expansion field. M 83 fits onto the local mean Hubble flow line of the velocity-distance relation (with H_0 ~ 60) with no significant deviation, supporting the earlier conclusion that the local velocity expansion field is remarkably cold on a scale of 10 Mpc, contrary to the predictions of the simplest cold dark matter model for large scale structure. The role of a cosmological constant has been invoked as a possible solution in providing a nearly uniform force field everywhere in the presence of a lumpy galaxy distribution. (abridged)

astro-ph↗

arXiv2002

Absolute Proper Motions to B~22.5: V. Detection of Sagittarius Dwarf Spheroidal Debris in the Direction of the Galactic Anticenter

We have detected a population of predominantly blue (B-V <= 1.1) stars in the direction l = 167 deg., b = -35 deg. (Kapteyn Selected Area 71) that cannot be accounted for by standard starcount models. Down to V ~ 20, the colors and magnitudes of these stars are similar to those of the southern overdensity detected by the Sloan Digital Sky Survey, and identified as stripped material from the Sagittarius dwarf spheroidal galaxy. We present absolute proper motions for the stars in SA 71, and we find that the excess blue stars represent a distinct, kinematically cooler component than the Galactic field, and in reasonable agreement with predictions of Sgr disruption models. The density of the excess SA 71 stars at V ~ 18.8 and B-V <=1.1 is within a factor of two of the density of the SDSS-south Sgr stripped material, and of that predicted by the Helmi and White disruption model. Three additional anticenter fields (SA 29, 45 and 118) show very good agreement with standard starcount models.

astro-ph↗

arXiv2002

Bias Properties of Extragalactic Distance Indicators.XI. Methods to Correct for Observational Selection Bias for RR Lyrae Absolute Magnitudes from Trigonometric Parallaxes Expected from the FAME Astrometric Satellite

Please note that this abstract has been shortened from that found in the paper. A brief history is given of the development of the correction for observation selection bias inherent in the calibration of absolute magnitudes using trigonometric parallaxes. As a tutorial to gain an intuitive understanding of several complicated trigonometric bias problems, we study a toy bias model of a parallax catalog which incorporates assumed parallax measuring errors of various severities. The two effects of bias errors on the derived absolute magnitudes are (1) the Lutz-Kelker correction itself that depends on the fractional parallax error and the spatial distribution, and (2) a Malmquist-like `incompleteness' correction of opposite sign due to various apparent magnitude cut-offs as they are progressively imposed on the catalog. The simulations involve 3 million stars spread with varying density distributions in a volume bounded by a radius of 50,000 pc. A fixed absolute magnitude of M_V = +0.6 is used to imitate RR Lyrae variables in the mean. The bias is demonstrated for various assumed spatial densities and parallax error models, including one that is projected for the FAME satellite. The effects of imposing magnit ude limits and limits on the `observer's' error are displayed. We contrast the method of calculating mean absolute magnitude directly from the parallaxes where bias corrections are mandatory, with an inverse method using maximum likelihood which is free of the Lutz-Kelker bias, although a Malmquist bias is present. We discuss the level of accuracy that can be expected in a calibration of RR Lyrae absolute magnitudes from the FAME data over the metallicity range of [Fe/H] from 0 to -2, given the known frequency of the local RR Lyraes closer than 1.5 kpc.

astro-ph↗

arXiv2001

Cepheid Calibration of the Peak Brightness of SNe Ia. XI. SN 1998aq in NGC 3982

Repeated imaging observations have been made of NGC 3982 with the Hubble Space Telescope between March and May 2000, over an interval of 53 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the type Ia supernova SN1998aq. A total of 26 Cepheid candidates were identified, with periods ranging from 10 to 45 days, using photometry with the DoPHOT program. The de-reddened distance to NGC 3982 is estimated from these data using various criteria to maximize signal to noise and reliability: the values lie between 31.71 and 31.82, with uncertainties in the mean of typically +/- 0.14 mag for each case. A parallel analysis using photometry with HSTphot discovered 13 variables, yielding a distance modulus of 31.85 +/- 0.16. The final adopted modulus is (M-m)_0 = 31.72 +/- 0.14 (22 +/- 1.5 Mpc). Photometry of 1998aq that is available in the literature is used in combination with the derived distance to NGC 3982 to obtain the peak absolute magnitude of this supernova. The lower limit (no extinction within the host galaxy) for M_V is -19.47 +/- 0.15 mag. Corrections for decline rate and intrinsic color to carry these to the reduced system of Parodi et al. (2000) have been performed. The derived luminosities at hand are fully consistent with the mean of the 8 normal SNe Ia previously calibrated with Cepheids. Together they yield H_0 ~ 60 +/- 2 (internal) km s-1 Mpc-1 based on an assumed LMC distance modulus of 18.50. We point out that correcting some of the systematic errors and including uncertainty estimates due to them leads to H_0 = 58.7 +/- 6.3 (internal) km s-1 Mpc-1.

astro-ph↗

arXiv2001

The Tolman Surface Brightness Test for the Reality of the Expansion. III. HST Profile and Surface Brightness Data for Early-Type Galaxies in Three High-Redshift Clusters

Photometric data for 34 early-type galaxies in the three high-redshift clusters Cl 1324+3011 (z = 0.76), Cl 1604+4304 (z = 0.90), and Cl 1604+4321 (z = 0.92), observed with the Hubble Space Telescope (HST) and with the Keck 10-meter telescopes by Oke, Postman & Lubin, are analyzed to obtain the photometric parameters of mean surface brightness, magnitudes for the growth curves, and angular radii at various Petrosian eta radii. The angular radii at eta = 1.3 mag for the program galaxies are all larger than 0.24". All of the galaxies are well resolved at this angular size using HST whose point-spread function is 0.05", half width at half maximum. The data for each of the program galaxies are listed at eta = 1.0, 1.3, 1.5, 1.7, and 2.0 mag. They are corrected by color equations and K terms for the effects of redshift to the rest-frame Cape/Cousins I for Cl 1324+3011 and Cl 1604+4304 and R for Cl 1604+4321. The K corrections are calculated from synthetic spectral energy distributions derived from evolving stellar population models of Bruzual & Charlot which have been fitted to the observed broad-band (BVRI) AB magnitudes of each program galaxy. The listed photometric data are independent of all cosmological parameters. They are the source data for the Tolman surface brightness test made in Paper IV.

astro-ph↗

arXiv2001

The Tolman Surface Brightness Test for the Reality of the Expansion. IV. A Measurement of the Tolman Signal and the Luminosity Evolution of Early-Type Galaxies

We review a sample of the early literature in which the reality of the expansion is discussed, explain Hubble's reticence to accept the expansion as real, and contrast the Tolman surface brightness test with three other modern tests. We search for the Tolman surface brightness depression with redshift using the Hubble Space Telescope (HST) data from Paper III for 34 early-type galaxies from the three clusters Cl 1324+3011 (z=0.76), Cl 1604+4304 (z=0.90), and Cl 1604+4321 (z=0.92). Depressions of the surface brightness relative to the zero-redshift fiducial lines in the mean surface brightness, log linear radius diagrams of Paper I are found for all three clusters. Expressed as the exponent, n, in 2.5 log (1 + z)^n mag, the value of n for all three clusters is n = 2.59 +/- 0.17 in the R band and 3.37 +/- 0.13 in the I band for a q_o = 1/2 model. The sensitivity of the result to the assumed value of q_o is shown to be less than 23% between q_o = 0 and +1. For a true Tolman signal with n = 4, the luminosity evolution in the look-back time, expressed as the exponent in 2.5 log (1+z)^(4-n) mag, must then be between 1.72 to 1.19 in the R band and 0.94 to 0.45 in the I band. We show that this is precisely the range expected from the evolutionary models of Bruzual & Charlot. We conclude that the Tolman surface brightness test is consistent with the reality of the expansion. We have also used the high-redshift HST data to test the ``tired light'' speculation for a non-expansion model for the redshift. The HST data rule out the ``tired light'' model at a significance level of better than 10 sigma.

astro-ph↗

arXiv2001

The Tolman Surface Brightness Test for the Reality of the Expansion. I. Calibration of the Necessary Local Parameters

The extensive CCD photometry by Postman & Lauer (1995, ApJ, 440, 28) in the Cape/Cousins R photometric band for first ranked cluster elliptical and S0 galaxies in 118 low redshift clusters is analyzed for the correlations between average surface brightness, linear radius, and absolute magnitude. The purpose is to calibrate the correlations between these three parameters in the limit of zero redshift. These local correlations provide the comparisons to be made in Paper IV with the sample of early-type galaxies at high redshift in search of the Tolman surface brightness signal of (1 + z)^4 if the expansion is real. Surface brightness averages are calculated at various metric radii in each galaxy in the sample. The definition of such radii by Petrosian (1976, ApJ, 209, L1) uses ratios of observed surface photometric data. The observed surface brightnesses are listed for 118 first ranked cluster galaxies at Petrosian eta radii of 1.0, 1.3, 1.5, 1.7, 2.0, and 2.5 mag. The three local diagnostic correlation diagrams are defined and discussed. We review the Tolman test and show that, although recipes from the standard cosmological model that already have the Tolman signal incorporated are required to calculate linear radii and absolute magnitudes from the observed data, the test is nevertheless free from the hermeneutical circularity dilemma occasionally claimed in the literature. The reasons are the observed mean surface brightness (1) is independent of any assumptions of cosmological model, (2) does not depend on the existence of a Tolman signal because it is calculated directly from the data using only angular radii and apparent magnitudes, and (3) can be used to search for the Tolman signal because it carries the bulk of that signal.

astro-ph↗

arXiv2001

The Tolman Surface Brightness Test for the Reality of the Expansion. II. The Effect of the Point-Spread Function and Galaxy Ellipticity on the Derived Photometric Parameters

To complete the Tolman surface brightness test on the reality of the expansion of the Universe, we need to measure accurately the surface brightness profiles of the high-redshift galaxy sample. We, therefore, investigate the effects of various sizes of point-spread-functions composed of telescope diffraction, CCD pixel resolutions, and ground-based seeing on the measurements of mean surface brightness. We have done the calculations using two synthetic galaxies of effective radii of 0.70" and 0.25" with point-spread functions of 0.1, 0.3, and 0.9 arcseconds. We have also compared actual observations of three high-redshift galaxies in the cluster Cl 1324 + 3011 (z = 0.76) made both with the Keck telescopes in seeing of about 0.9" and with HST which has a PSF that is approximately ten times smaller. The conclusion is that HST data can be used as far into the galaxy image as a Petrosian metric radius of eta = 1.3 magnitudes, whereas the ground-based data will have systematic errors of up to 2.9 magnitudes in the mean surface brightness at eta values of less than 2.2 magnitudes. In the final section, we compare the differences in derived average surface brightness for nearly circular galaxy images compared with highly flattened images. The comparison is made by using the two reduction procedures of (1) integrating the profile curves using circular apertures, and (2) approximating an ``equivalent circular'' galaxy that is highly elongated by using an ``effective'' radius of sqrt{ab}, where a and b are the semi-major and semi-minor axis, respectively, of the best-fitting ellipse. The conclusion is that the two methods of reduction give nearly identical results and that either method can be used to analyze the low and high-redshift galaxy samples used in the Tolman test.

astro-ph↗

arXiv1999

The Early Palomar Program (1950-1955) for the Discovery of Classical Novae in M81: Analysis of the Spatial Distribution, Magnitude Distribution, and Distance Suggestion

Data obtained in the 1950-1955 Palomar campaign for the discovery of classical novae in M81 are set out in detail. Positions and apparent B magnitudes are listed for the 23 novae that were found. There is modest evidence that the spatial distribution of the novae does not track the B brightness distribution of either the total light or the light beyond an isophotal radius that is $70\arcsec$ from the center of M81. The nova distribution is more extended than the aforementioned light, with a significant fraction of the sample appearing in the outer disk/spiral arm region. We suggest that many (perhaps a majority) of the M81 novae that are observed at any given epoch (compared with say $10^{10}$ years ago) are daughters of Population I interacting binaries. The conclusion that the present day novae are drawn from two population groups, one from low mass white dwarf secondaries of close binaries identified with the bulge/thick disk population, and the other from massive white dwarf secondaries identified with the outer thin disk/spiral arm population, is discussed. We conclude that the M81 data are consistent with the two population division as argued previously from (1) the observational studies on other grounds by Della Valle et al. (1992, 1994), Della Valle & Livio (1998), and Shafter et al. (1996) of nearby galaxies, (2) the Hatano et al. (1997a,b) Monte Carlo simulations of novae in M31 and in the Galaxy, and (3) the Yungelson et al. (1997) population synthesis modeling of nova binaries. Two different methods of using M81 novae as distance indicators give a nova distance modulus for M81 as $(m-M)_0 = 27.75$, consistent with the Cepheid modulus that is the same value.

astro-ph↗