arXiv subjects

G. A. Tammann

Publications and source records attributed to G. A. Tammann.

At least 37 records · Page 2Linked to original sources

arXiv2003

New Period-Luminosity and Period-Color Relations of Classical Cepheids: I. Cepheids in the Galaxy

321 Galactic fundamental-mode Cepheids with good B,V,I photometry by Berdnikov et al. 2000 and with homogenized color excesses E(B-V) based on Fernie et al. 1995 are used to determine their P-C relation in the range 0.4<log P<1.6. Distances of 25 Cepheids in open clusters (Feast 1999) and of 28 Cepheids with BBW distances (Gieren et al. 1998) are used in a first step to determine the absorption coefficients R_B=4.17, R_V=3.17, and R_I=1.89. The two sets define two independent P-L relations which agree very well in slope. They are therefore combined into a single mean Galactic P-L relation. Galactic Cepheids are redder in (B-V) than those in LMC and SMC as shown by the over 1000 Cloud Cepheids with good standard B,V,I photometry by Udalski et al 1999. Also the (B-V), (V-I) two-color diagrams differ between Cepheids in the Galaxy and the Clouds, attributed both to the effects of metallicity differences, on the spectral energy distributions of the Cepheids and to a shift in the effective temperature of the middle of the instability strip for LMC and SMC relative to the Galaxy by about Delta log Te ~ 0.02 at M_V=-4.0 mag, hotter for both LMC and SMC. Differences in the P-C relations between the Galaxy and the Clouds show that there cannot be a universal P-L relation from galaxy-to-galaxy in any given color. The inferred non-uniqueness of the slope of the P-L relations in the Galaxy, LMC, and SMC is born out by the observations. The Cloud Cepheids follow a shallower overall slope of the P-L relations in B,V,I than the Galactic ones. LMC and SMC Cepheids are brighter in V than in the Galaxy by up to 0.5 mag at short periods and fainter at long periods.

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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)

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arXiv2002

GAIA and the Extragalactic Distance Scale

The local (v<1200kms) and the cosmic expansion field out to 30000kms-1 are characterized by Ho=58. While the random error is small (+-2), it may still be affected by systematic errors as large as 10%. The local expansion is outlined by Cepheids and by Cepheid-calibrated TF distances of a complete sample of field galaxies and by nearby groups and clusters; the cosmic expansion is defined by Cepheid-calibrated SNeIa. The main source of systematic errors are therefore the shape and the zero point of the P-L relation of Cepheids and its possible dependence on metallicity. GAIA will essentially eliminate these error sources. Another source of systematic error is due to the homogenization of SNeIa as to decline rate Delta m_15 and color (B-V). GAIA will discover about half of the 2200 SNeIa which will occur during a four-year lifetime within 10000kms. For many of them ground-based follow-up will provide useful photometric parameters (and spectra), which will allow to fix the dependence of the SNeIa luminosity on Delta m_15 and (B-V) with high accuracy. At the same time they will yield exquisite distances to an corresponding number of field galaxies. - GAIA will also revolutionize the very local distance scale by determining fundamental distances of the companion galaxies of the Milky Way and even of some spirals in- and possibly outside the Local Group from their rotation curves seen in radial velocities and proper motions. Moreover, GAIA will obtain trigonometric parallaxes of RR Lyrae stars, of red giants defining the TRGB, of stars on the ZAMS, of White Dwarf defining their cooling sequence, and of globular clusters, and determine the metallicity dependence of these distance indicators. It will thus establish a self-controlling network of distance indicators within the Local Group and beyond.

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arXiv2002

Cosmic Expansion and Ho: A Retro- and Pro-Spective Note

Attempts to measure extragalactic distances over the last 90 years are briefly described. It follows a short history of the discovery of the expansion of space. Reasons are discussed for the decrease of the Hubble constant from Ho~500 originally to Ho<~60 at present. Remaining problems with Cepheids as local distance calibrators are outlined.

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arXiv2001

Cepheids, Supernovae, Ho, and the Age of the Universe

The local expansion field is mapped using Cepheids, a complete sample of TF distances, and nearby cluster distances. The large-scale field is mapped using Cepheid-calibrated blue SNeIa. These data give Ho(local)=59.2+/-1.4 [km/s Mpc^-1] and Ho(cosmic)=57.4+/-2.3. The intermediate expansion field (1200 < v < 10000km/s) is less well calibrated but fully consistent with Ho~60. Ho is therefore (nearly) scale-invariant (high-density regions excluded). -- The P-L relation of Cepheids is based on an improved zero point of (m-M)_{LMC}=18.56. The slope of the P-L relation for P>10days, as judged from OGLE data (Udalski et al. 1999) is flatter than anticipated, which tends to increase the above values of Ho by 3.4 units. No significant metallicity effect on the Cepheid distances seems to be indicated. For all practical purposes Ho=60 is recommended with a systematic error of probably less than 10%. -- The corresponding expansion age is T=15.7+/-1.5Gy (with Omega(Matter)=0.3, Omega(Lambda)=0.7), which compares well with the formation time of 15+/-2Gy for the apparently oldest globular cluster M107.

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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.

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arXiv2000

Cepheid Calibration of the Peak Brightness of SNe Ia. X. SN 1991T in NGC 4527

Repeated imaging observations have been made of NGC 4527 with the Hubble Space Telescope between April and June 1999, over an interval of 69 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 SN1991T, which showed relatively unusual behavior by having both an abnormal spectrum near light maximum, and a slower declining light curve than the proto-typical Branch normal SNe Ia. A total of 86 variables that are putative Cepheids have been found, with periods ranging from 7.4 days to over 70 days. From photometry with the DoPHOT program, the de-reddened distance modulus is determined to be (m-M)_0 = 30.67 +/- 0.12 (internal uncertainty) using a subset of the Cepheid data whose reddening and error parameters are secure. A parallel analysis of the Cepheids using photometry with ROMAFOT yields (m -M)_0 =30.82 +/- 0.11. The final adopted modulus is (m -M)_0 =30.74 +/- 0.12 +/- 0.12 (d=14.1 +/- 0.8 +/- 0.8 Mpc). The photometric data for SN1991T are used in combination with the Cepheid distance to NGC 4527 to obtain the absolute magnitude for this supernova of M_V^0(max) = -19.85 +/- 0.29. The relatively large uncertainty is a result of the range in estimates of the reddening to the supernova. Thus SN1991T is seen to be only moderately brighter (by ~ 0.3 mag) than the mean for spectroscopically normal supernovae, although magnitude differences of up to 0.6 mag cannot be ruled out.

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arXiv2000

Ho from Type Ia Supernovae

The Hubble diagrams in B, V, and I of a complete sample of 35 SNeIa with (B-V) < 0.06 and 1200 < v < 30000 kms^{-1} have a scatter of only 0.1 mag, after small corrections are applied for differences in decline rate Delta m_{15} and color (B-V). The tightness of the Hubble diagrams proves blue SNeIa to be the best ``standard candles'' known. Their absolute magnitudes M_{B,V,I} are calibrated by eight SNeIa with Cepheid distances from HST. Combining this calibration with the appropriate Hubble diagrams yields a large-scale value of H_0 = 58.5+/-6.3 at the 90-percent confidence level. The Hubble diagram of SNeIa has so small scatter that it seems feasable to determine Lambda ``locally'', i.e. within z<0.12, once 100-200 SNeIa with good photometry will be available. Such a local determination would minimize evolutionary effects and K-term corrections.

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arXiv2000

Supernova type Ia luminosities, their dependence on second parameters, and the value of H_0

A sample of 35 SNe Ia with good to excellent photometry in B and V, minimum internal absorption, and 1200 < v < \approx 30000 km/s is compiled from the literature. As far as their spectra are known they are all Branch-normal. For 29 of the SNe Ia also peak magnitudes in I are known. The SNe Ia have uniform colors at maximum, i.e. =-0.012 mag (sigma=0.051) and =-0.276 mag (sigma=0.078). In the Hubble diagram they define a Hubble line with a scatter of $σ_M$=0.21-0.16 mag, decreasing with wavelength. The scatter is further reduced if the SNe Ia are corrected for differences in decline rate Delta_m_15 or color (B-V). A combined correction reduces the scatter to sigma<=0.13 mag. After the correction no significant dependence remains on Hubble type or galactocentric distance. The Hubble line suggests some curvature which can be differently interpreted. A consistent solution is obtained for a cosmological model with Omega_M=0.3, Omega_Lambda=0.7, which is indicated also by much more distant SNe Ia. Absolute magnitudes are available for eight equally blue (Branch-normal) SNe Ia in spirals, whose Cepheid distances are known. If their well defined mean values of M_B, M_V, and M_I are used to fit the Hubble line to the above sample of SNe Ia one obtains H_0=58.3 km/s/Mpc, or, after adjusting all SNe Ia to the average values of Delta_m_15 and (B-V), H_0=60.9 km/s/Mpc. Various systematic errors are discussed whose elimination tends to decrease H_0. The finally adopted value at the 90-percent level, including random and systematic errors, is H_0=58.5 +/- 6.3 km/s/Mpc. Several higher values of H_0 from SNe Ia, as suggested in the literature, are found to depend on large corrections for variations of the light curve parameter and/or on an unwarranted reduction of the Cepheid distances of the calibrating SNe Ia.

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arXiv1999

The Status of the Distance Scale

Cepheids are the pillar of the extragalactic distance scale, but their reach in distance is not sufficient to calibrate H_0. Yet HST has provided Cepheid distances to eight galaxies which have produced SNe Ia. The latter are used as nearly perfect standard candles to carry the distance scale to 30,000 km/s, giving H_0 = 58 +/- 5. This determination finds support in other methods but its range in distance and its weight is unparalleled.

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arXiv1999

Cepheid Calibration of the Peak Brightness of SNe Ia -- IX. SN 1989B in NGC 3627

(Abridged) Repeated imaging observations have been made of NGC 3627 with the HST in 1997/98, over an interval of 58 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the prototypical, `Branch normal', type Ia supernova SN 1989B. A total of 83 variables have been found, of which 68 are definite Cepheid variables with periods ranging from 75 days to 3.85 days. The de-reddened distance modulus is determined to be (m-M)_0= 30.22+/-0.12 (internal uncertainty) using a subset of the Cepheid data whose reddening and error parameters are secure. The photometric data of Wells et al. (1994), combined with the Cepheid data for NGC 3627 give M_B(max)= -19.36+/-0.18 and M_V(max)= -19.34+/-0.16 for SN 1989B. Combined with the previous six calibrations in this program, plus two additional calibrations determined by others gives the mean absolute magnitudes at maximum of = -19.48+/-0.07 and = -19.48 +/-0.07 for `Branch normal' SNe Ia at this interim stage in the calibration program. The second parameter correlations of M(max) of blue SNe Ia with decay rate, color at maximum, and Hubble type are re-investigated. The dependence of on decay rate is non-linear, showing a minimum for decay rates between 1.0< Delta m_15 <1.6. Magnitudes corrected for decay rate show no dependence on Hubble type, but a dependence on color remains. Correcting both the fiducial sample of 34 SNe Ia with decay-rate data and the current 8 calibrating SNe Ia for the correlation with decay rate as well as color gives H_0= 60+/-2 (internal) km/s/Mpc, in both B and V. The same value to within 4% is obtained if only the SNe Ia in spirals (without second parameter corrections) are considered.

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arXiv1999

The Distance of the Virgo Cluster

Six different distance determination methods of Virgo cluster members yield a mean distance modulus of (m-M)^0(Virgo) = 31.60 +/- 0.09 (20.9 +/- 0.9 Mpc). This value can be carried out to > 10,000 km/s by means of 31 clusters whose distances are well known relative to the Virgo cluster. They yield H_0 = 56 +/- 4 (random error) +/- 6 (systematic error), independent of local streaming motions.

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arXiv1999

The Luminosity Calibration of SNe Ia: Present Status

Blue Supernovae of Type Ia (SNe Ia) have become the most important objects in cosmology being of exceptionally uniform luminosity. Used as relative distance indicators they map deviations from pure Hubble flow and determine the cosmological constant Lambda. Once their absolute magnitude is determined they provide the best estimate of the large-scale value of the Hubble constant H_0. An HST project is reviewed where Cepheid distances are used for the luminosity calibration of SNe Ia. The mean luminosity of 8 SNe Ia is M_B(max)= -19.47 +/- 0.07, M_V(max)= -19.48 +/- 0.07, corresponding -- after small corrections for second parameters -- to H_0(cosmic)= 59 +/- 5.

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arXiv1999

The Luminosity Function of Globular Clusters as an Extragalactic Distance Indicator

The absolute magnitude M* of the peak of the globular cluster luminosity function (GCLF), approximated by a Gaussian, can be calibrated independently in the Galaxy and M 31 through RR Lyr stars and Cepheids, respectively. They yield, in perfect agreement, M*_B = -6.93+-0.08 and M*_V = -7.62+-0.08. Application of these values to the GCLFs in the Leo Group (n=2), the Virgo cluster (n=8), and the Coma cluster (n=2) gives distances which agree with the best determinations from other methods. However, the corresponding distance of the Fornax cluster (n=7) is significantly underestimated, and the distances of several field galaxies are inconsistent. A second parameter, like the width of the GCLF or the color of the peak, is apparently needed to control differences in the GC formation history.

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arXiv1998

Variations of the Cosmic Expansion Field and the Value of the Hubble Constant

Four Hubble diagrams are combined to test for the linearity of the cosmic expansion field. The expansion rate, H_0, is found to decrease by ~5% out to 18000km/s. Beyond this distance the mean value of H_0 is close to the value at 10000km/s. The absolute value of H_0 is derived in two different ways. The one leads through Cepheids from HST and blue SNe Ia to H_0=57+/-7 (external error) at 30000km/s. The other uses various distance indicators to the Virgo cluster whose distance can be extended to 10000km/s by means of only relative cluster distances; the result of H_0 is closely the same. Independent distances from purely physical methods (SZ effect, gravitational lenses, and MBW fluctuations) cluster about H_0(cosmic)=58.

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arXiv1998

The Linearity of the Cosmic Expansion Field and the Value of the Hubble Constant

A linearity test shows H_0 to decrease by 7% out to 18000 km/s. The value at 10000 km/s is a good approximation to the mean value of Ho over very large scales. The construction of the extragalactic distance scale is discussed. Field galaxies, cluster distances relative to Virgo, and blue supernovae of type Ia yield Ho(cosmic) with increasing weight; they give consistently H_0=57+/-7 (external error). This value is supported by purely physical distance determinations (SZ effect, gravitational lenses, MWB fluctuations). Arguments for H_0>70 are discussed and shown to be flawed.

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arXiv1997

The Virgo cluster distance from 21 cm-line widths

The distance of the Virgo cluster is derived in the B band from the 21 cm-line width-absolute magnitude relation. The latter is calibrated using 18 spirals with Cepheid distances mainly from HST. The calibration is applied to a complete sample of non-peculiar spirals with i>45 deg and lying within the optical (n=49) or X-ray (n=35) contour of the cluster, resulting in a mean cluster distance of (m-M)_0=31.58+/-0.24 mag (external error) or 20.7+/-2.4 Mpc. The mean distance of subcluster A is 0.46+/-0.18 mag smaller than that of subcluster B, but the individual distances of the members of the two substructures show considerable overlap. The distance modulus is corrected by -0.07 mag for the fact that cluster members have lower H I-surface fluxes and are redder in (B-I) at a given line width than the (field) calibrators. Different sources of the B magnitudes and line widths have little effect on the resulting distance. Different precepts for the internal-absorption correction change the result by no more than +/-0.17 mag. The individual distances of the cluster members do not show any dependence on recession velocity, inclination, Hubble type or line width. The dependence on apparent magnitude reflects the considerable depth effect of the cluster. The adopted distance is in good agreement with independent distance determinations of the cluster. Combining the cluster distance with the corrected cluster velocity of 1142+/-61 km/s gives H_0=55+/-7 km/s/Mpc (external error). If the Virgo cluster distance is inserted into the tight Hubble diagram of clusters out to 11000 km/s using relative distances to the Virgo cluster one obtains a global value of H_0=57+/-7 km/s/Mpc.

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arXiv1996

The evidence for the long distance scale with H_0<65

The status of the determination of the Hubble constant is reviewed, setting out the evidence for the long distance scale with H_0=55+/-5. In parallel, various precepts said to favor the short distance scale with H_0>70 are discussed. The strongest evidence for the long scale are (1) the calibration of the peak absolute magnitude of type Ia supernovae with their Hubble diagram, (2) the distance to the Virgo cluster by six largely independent methods, and (3) field spirals binned by luminosity class. The three methods give H_0=56+/-3, 55+/-2, and 53+/-3 (internal errors). H_0 does not vary significantly over scales from 10-500 Mpc. Higher values of H_0 still in the literature are based on (1) an untenably small distance to the Virgo cluster, (2) an untenably large Virgo cluster velocity, (3) a questionable route through the Coma cluster, (4) an incorrect precept that the Cepheid distance to NGC 1365 gives the distance to NGC 1613, parent to two SNe Ia, calibrating them, (5) an unjustified reliance on planetary nebulae and surface brightness fluctuations as distance indicators, and (6) either an underestimation or a neglect of the importance of observational selection bias in flux-limited samples. There is no valid evidence for H_0>70. The status of the time scale test is reviewed. The result is 13-14 (+/-2) Gyr for the age of the Galactic globular cluster system. There is no time scale crisis provided that q_0<0.3, H_0=55, and Lambda=0.

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