arXiv:astro-ph/9805024v1 4 May 1998

o.Nt .Ato.Soc. Astron. R. Not. Mon. .DlaValle H Della of M. Value the the and of Brightness 1992A Supernova Peak Ia the Type of Calibration Cluster Globular 4 3 2 1 5 1Ags 2018 August 11 NIahv ml iprin fteodrof order of the maximum of at dispersion, magnitudes small absolute a have the were SNeI-a that (1995)] show al. et to (1990), Vaughan able Branch (1992), Panagia and and Miller Valle Della Lei (1990), on [e.g. Tammann mainly authors of and past, number bundgut a recent data, the photographic of In basis the candles. standard reliable as important is light maximum reasons. at two Ia for Supernovae of study The INTRODUCTION 1 rvd itnemaueet iha netit fonly could of uncertainty objects an these with candles, measurements standard distance provide as used principle, In ewe h boueMgiuea aiu ftp Ia type of Maximum relationship at a Magnitude of Absolute existence the possible between the Pskovski concerning by suggestion (1967) former SNeI-a has a light, of strengthened maximum sample at considerably a sampled of well were basis light-curves the whose ‘idyll on previous (1993), the Phillips complicate to scenario. appear years, 6–7 last the c srpyiaice ntttPtdm ndrSenat 1 Sternwarte der An 34131, Potsdam, 11, Institut Tiepolo Astrophysikalisches Cru via Santa Trieste, Astronomico, California, dell Osservatorio of Vicolo University Padova, Observatory, of UCO/Lick University Astronomy, of Department uoenSuhr bevtr,Aos eCroa30,Vit 3107, Cordoba de Alonso Observatory, Southern European ∼ < 00RAS 0000 ± nteoehn uenveI r omnyregarded commonly are Ia Supernovae hand one the On 4.Hwvr hg–ult’osrain,otie in obtained observations, ‘high–quality’ However, 14%. 1 .Kissler-Patig M. , 000 0–0 00)Pitd1 uut21 M L (MN 2018 August 11 Printed (0000) 000–000 , bouemgiueo N19Aa aiu fM of maximum at 1992A SN following of The 18.6 magnitude budget. of absolute error 1380 with NGC systematic made to and been distance random has complete results mag the HIPPARCOS turn–over latest of the Functio of the Luminosity peak using the clusters Cluster of Way 199 recalibration Globular SN A the 1380. of NGC light of galaxy, maximum magnitude at turn–over magnitude the absolute the determined have We ABSTRACT e:gnrl itnescale. distance general, ter: otdsatSeo h aa-ooosre,yed H yields survey, Calan-Tololo relationship, the this t of of SNe on calibration distant maximum, new most at The Cepheid Function. magnitude with Luminosity obtained (1993 absolute been Cluster have Phillips’s the distances the individual and whose implicatio discuss decline SNeI-a, the also of fainter We discuss magnitude rate We explanations. a between half exist. possible than distances present more accurate and be which to for seems SNeI-a 1992A SN value, face e words: Key uenve niiul N19A uenve eea,Goua C Globular general, Supernovae: 1992A, SN individual: Supernovae: ∼ < 2 0 .Danziger J. , . mag. 3 ,D142 osa,Germany Potsdam, D-14482, 6, Trieste ic’ ,C 56,USA 95064, CA z, Osraoi ,312 Padova 35122, 5, ’Osservatorio - i cr,Csla101 atao Chile Santiago, 19001, Casilla acura, ± tr o yeI uenve ic h eklmnst is luminosity Cappella peak (e.g. mass the progen- nickel synthesized Since the the Supernovae. of to al. Ia uniqueness proportional et type the Della Wang for question 1997a, 1994, which itors al. al. of et et all Cappellaro Bartunov 1997), 1994, (e.g. Livio and rate occurrence their Valle of 1996), al. place et Riess Bergh and 1996, den Suntzeff van 1992, 1992, Pazder Pierce photomet- and and and Bergh 1994), den al. (van et evolution Nugent ric 1993, Bergh Branch den 1989, van Filippenko and early 1988, Jeffery and and intrinsic spectrosc Drucker spirals their (Branch, significant concern in observations of these occurring galaxies: existence type SNeI-a the between out differences pointed have ies 1995). al. et Hamuy 1998, (Lanoix NIavre between varies SNeI-a o bet ofimtePilp’ eainhp saconse- a As of value relationship. the uncertainties, Phillips’s these we the of (1996) quence confirm al. to et Sandage able Finally, not spirals. in Ia than fainter igi al yeglxe r naverage on are galaxies type early occur- SNeI-a in that ring found have (1996) Branch, Baron (=AMMRD). and Decline Romanishin of Rate their and Supernovae 1 . p,crepnigt (m–M)=31.35 to corresponding Mpc, 4 nteohrhn,anme fosrainlstud- observational of number a hand, other the On 3 .Storm J. & A T E tl l v1.4) file style X B ∼ mx = (max) 4 ◦ 0adams 0k s km 70 almost and 50 , 62 = 5 ◦ ± − ms km 6 18 . iueo h Milky the of nitude 79 n h Globular the and s eut mre a emerge: results H ∼ ± so hsresult this of ns − ◦ fisparent its of n hnteother the than 0 0 ple othe to applied nassessment an 1 ± relationship ) esrdwith measured . . ebsso 9 of basis he magnitudes 3 6 ae at Taken 16. Mpc 0 Ab using by 2A . 6 n an and 16, − 1 − Mpc 1 . opic lus- − ro re 1 2 M. Della Valle et al. et al. 1997b), one of the most direct observational ways to Table 1. Globular cluster luminosity functions in B, V , and R prove the existence of intrinsic differences between the pro- with the completeness factor genitors is to measure the differences in absolute magnitude at maximum for a sample of SNeI-a. Such differences might B counts comp V counts comp R counts comp then be attributed to either differences among the progeni- tors (Branch et al. 1995 for a review) and/or to differences 20.35 0. 1. 20.35 0. 1. 20.35 0. 1. 20.7 0. 1. 20.7 0. 1. 20.7 2. 1. in the mechanism of the explosion (e.g. Canal, Isern and 21.05 0. 1. 21.05 1. 1. 21.05 7. 1. Lopez 1988). 21.4 0. 1. 21.4 5. 1. 21.4 8. 1. These problems have motivated our study of SN 1992A. 21.75 1. 1. 21.75 7. 1. 21.75 30. 1. In section 2, we will briefly discuss the data and methods 22.1 2. 1. 22.1 17. 1. 22.1 35.4 0.96 which we have used to determine the turn–over magnitude 22.45 7. 1. 22.45 28.0 0.96 22.45 46.0 0.96 of the Globular Cluster Luminosity Function (=GCLF) of 22.8 15. 1. 22.8 45.0 0.96 22.8 48.3 0.93 NGC 1380. In section 3, we determine the distance to NGC 23.15 26.9 0.97 23.15 56.3 0.94 23.15 80.4 0.91 1380 and in section 4 we derive the absolute magnitude at 23.5 40.8 0.96 23.5 56.4 0.92 23.5 46.3 0.84 maximum light for SN 1992A. In section 5 we determine 23.85 47.3 0.95 23.85 66.6 0.87 23.85 45.3 0.70 the AMMRD. In section 6 we discuss the results and the 24.2 73.4 0.93 24.2 52.5 0.78 24.2 46.6 0.45 24.55 52.8 0.89 24.55 48.6 0.60 24.55 17.8 0.17 possible implications for the calibration of the extragalactic 24.9 59.0 0.81 24.9 23.0 0.26 24.9 – – distance scale and in the final section (7) we summarize our 25.25 39.4 0.66 25.25 – – 25.25 – – conclusions. 25.6 42.2 0.35 25.6 – – 25.6 – –

2.2 Computing the luminosity function 2 THE GLOBULAR CLUSTER LUMINOSITY FUNCTION We binned the globular clusters into 0.35 mag bins, and plotted their number versus magnitude to obtain the lumi- nosity function. These luminosity functions in B, V , and 2.1 The data R are shown in Figs. 2, 3, and 4. The counts are given in Tab. 1, together with the completeness that we corrected The GCLF was determined on the basis of data obtained for. Note that no completeness correction exceeding 10% at the ESO New Technology Telescope (NTT) using the was necessary until beyond the turn–over. Furthermore we ESO Multi-Mode Instrument (EMMI) in December 1993. only considered globular clusters down to our 60% complete- The stacked frames of NGC 1380 totaled an equivalent ex- ness limit (25.3 mag in B, 24.2 mag in V , 23.9 mag in R) in posure time of 2700 sec in R, 7800 sec in V , and 15000 sec in the fits. B with an effective FWHM of stellar images ∼< 1.0 arcsec in all filters. The corrected field of view covered by all three filters was approximately 6.5 by 6.5 arcminutes. 2.3 Turn–over values in B, V , and R A comprehensive description of the data reduction is given in Kissler-Patig et al. (1997), where we fully analyze The globular cluster luminosity function is well represented the data on the globular cluster systems. In the present pa- by a Gaussian (Whitmore 1997 for the most recent review), per we concentrate on the turn-over magnitude of the glob- or a t5 function (Secker 1992, Kissler et al. 1994), with a ular cluster luminosity functions. universal absolute peak luminosity (see next paragraph). We Briefly, we modeled the galaxy light with isophotal mod- fitted both types of functions to our luminosity functions to els in all colours and subtracted it from the original frames derive the turn–over magnitudes and width simultaneously. (Fig. 1). The photometry was carried out on these flat back- The robustness of our result are tested in several ways. ground exposures with DAOPHOT operating in IRAF. Ar- We experimented with different binnings, varying the bin tificial star experiments with typically 20000 stars added in width and bin centers. We used subsamples of our globular each colour over many runs were carried out to determine clusters and computed their luminosity function. We fitted our finding completeness. Finally our B, V ,and R samples the luminosity function down to various magnitudes. Finally were combined (roughly 900 objects), point sources were se- we used different “combined” completeness factors (i.e. the lected (710 objects) and then selected in colour (422 objects) product of the completeness factors of different colours) as to reject fore- and back-ground objects. The globular cluster well as the completeness for individual colours. In all cases luminosity function was then computed with objects further we obtained similar results for the turn–over magnitudes than 35 arcsec and closer than 125 arcsec to the center of and distribution width within about 0.10 mag, independent the galaxy. The lower limit avoids incompleteness changes of the type of function used. This gives us confidence in the towards the center, the upper limit was the limit of the sur- results and provides a measure of the overall error of less face density profile of the globular clusters. Finally we linked than 0.10 mag. The results are tabulated in Tab. 2. our photometry for the globular clusters to the one used to Forcing a broad function (σGauss = 1.35) to our data, as derive the lightcurve of SN 1992A by adjusting our cali- proposed by Whitmore (1997) for bright ellipticals, pushes bration to match the comparison stars used by Cappellaro the turn–over values to ≈ 0.15 magnitudes fainter but results et al. (1997b). This required systematic shifts of +0.070 to in unaccetable fits. The width of the GCLF of NGC 1380 (an +0.095 in all colours after which the RMS scatter for the S0 galaxy) is in much better agreement with values found for comparison stars was 0.02 mag. the Milky Way and M31 (e.g. Secker 1992) and fainter early–

c 0000 RAS, MNRAS 000, 000–000 Globular Cluster Calibration of SN 1992A 3

Table 2. Turn–over values and width for the globular cluster Table 3. Turn–over values and dispersions of the Milky Way luminosity function in B, V , and R globular cluster luminosity function in B, V , and R derived from the McMaster University globular cluster database

Gaussian t5 function T–O mag σ T–O mag σ Colour TO value σGauss

B 24.38 ± 0.09 0.92 ± 0.10 24.38 ± 0.09 0.89 ± 0.10 B −7.08 ± 0.08 1.07 ± 0.08 V 23.67 ± 0.11 0.96 ± 0.10 23.69 ± 0.11 0.95 ± 0.10 V −7.62 ± 0.06 1.16 ± 0.09 R 23.16 ± 0.09 1.00 ± 0.10 23.17 ± 0.10 0.98 ± 0.10 R −8.14 ± 0.07 0.88 ± 0.11 type galaxies (Kissler et al. 1994, Kissler-Patig, Richtler, & had been measured with high precision by HIPPARCOS. Hilker 1996), supporting the result from our free fits. Their results support a dependence of the absolute hor- A previous determination of the V turn–over magni- izontal branch luminosity on the metallicity of the type: tude for NGC 1380 was made by Blakeslee & Tonry (1996), MV (HB) = 0.29(±0.09) · ([Fe/H]+1.5) + 0.43(±0.04). We 0 who derived a value of mV = 24.05 ± 0.25 in disagreement therefore decided to re-fit the GCLF of the Milky Way in B, with our results. However, it seems (Blakeslee priv. com. ) V , and R using the new distance implied by this relation. that from their V data alone, they could not correct for We used the McMaster globular cluster database (Har- a background cluster located about 30 arcsec East of NGC ris 1996) compiling data for 146 globular clusters in the 1380 (see Kissler-Patig et al. 1997). If we include these back- Milky Way. We corrected for reddening according to Rieke ground galaxies (having V magnitudes between 21 and 24 & Lebofsky (1985), and derived distances using the rela- mag), and compute the fit to their magnitude limit, we can tion mentioned above to derive absolute B, V and R mag- reproduce their result in the sense that our peak appears to nitudes for all clusters. The resulting luminosity functions be shifted by almost half a magnitude fainter. are shown in Fig. 5, together with the best Gaussian fits. The mean from various fits to different binnings with both Gaussian and t5 functions, and various subsamples (exclud- 3 THE DISTANCE TO NGC 1380 ing the most reddened clusters), are listed in Tab. 3, the errors are given as dispersions around the mean, without considering any systematic error. The errors in the individ- It is now well established that, excluding some small metal- ual determinations are typically of the order 0.07 mag, as licity and perhaps some galaxy–type effects, the absolute shown in the table. Varying the binning and subsamples turn–over of the GCLF is constant for the old clusters in results in typical errors of the same order, leading to a to- all galaxies (e.g. Whitmore 1997, Harris 1997). The abso- tal random error of 0.10 mag. However we have to account lute peak luminosity can be derived from “local” calibrators for any systematic error introduced by our MV (HB)–[Fe/H] such as the globular cluster systems of the Milky Way or relation. We therefore recomputed all distances for Fusi– M31. While comparing globular clusters in the Milky Way Pecci’s et al. (1996) relation, derived however from M31 clus- and M31 to those in bright ellipticals is often quoted as com- ters, and implying a much weaker metallicity dependence paring “apples with oranges”, because of possible globular [MV (HB) = 0.13(±0.07) · ([Fe/H]) + 0.95(±0.09)] (see also cluster population differences (“galaxy–type” effects), the Carney et al. 1992). We then derive mean turn–over val- comparison makes more sense in the case of NGC 1380 clas- ues systematically fainter by about 0.2 mag. The above two sified as an S0 galaxy. The colour distribution of the NGC relations span the range currently under debate. In the fol- 1380 globular clusters is similar to that of the Milky Way lowing we will adopt the relation derived for the Milky Way globular clusters (Kissler-Patig et al. 1997), including old clusters using the Gratton et al. (1997) relation, and keep blue halo clusters, and old red ”bulge” clusters, with only in mind a possible systematic error of the turn–over values the colour distribution in NGC 1380 extending further to of up to –0.2 mag. 0 the red. We shall shortly discuss the implications, but shall Our final result for the Milky Way [MV = −7.62±0.10] first review the absolute turn–over luminosities for the Milky compares well with the average of the values derived for M31 0 Way and M31 GCLF’s. by Secker (1992) and Sandage & Tammann (1995) (MV = Secker (1992) and Sandage & Tammann (1995) recently −7.61±0.13). By combining our Milky Way results with the 0 0 determined the turn–over values MV and MB for M31 and turn–over magnitudes of Tab. 2, we find (m−M)V = 31.29± 0 the Milky Way. They respectively found MV = −7.51±0.15 0.14, (m−M)B = 31.46±0.13, and (m−M)R = 31.30±0.13, 0 0 and MV = −7.29 ± 0.13, and MV = −7.70 ± 0.20 and (errors being random errors, not including up to –0.2 mag 0 MV = −7.60 ± 0.11 for M31 and the Milky Way. While systematic error). the peak of the GCLF in M31 depends “only” on the Two related effects have to be further considered: the adopted distance for Andromeda, the peak of the GCLF metallicity effect on the turn–over (metal rich globular clus- in the Milky Way depends on the distance moduli adopted ter having fainter absolute magnitude), and a galaxy–type for the individual clusters, i.e. for our purpose on the abso- effect. While the first one was well quantified by Ashman, lute magnitude of the horizontal branch and its metallicity Conti & Zepf (1995), the second effect rests on a less firm dependence. The former large uncertainties are reflected in base (Harris 1997), since it implies known distances to galax- the discrepant values of Secker and Sandage & Tammann. ies of different types with well observed GCLFs. While cen- However, recently Reid (1997) and Gratton et al. (1997) tral giant ellipticals might differ from other galaxies due to derived distances to several globular clusters by attaching their complex globular cluster system, it is not clear at all their main sequences to nearby subdwarfs whose parallaxes that GCLFs in spirals and small ellipticals differ systemat-

c 0000 RAS, MNRAS 000, 000–000 4 M. Della Valle et al. ically. The effect would be of the order of 0.1 mag between 1996). By assuming (m − M) = 31.35 ± 0.16, we find an ab- an S0 and a spiral in the sense that the S0 would have a solute magnitude at maximum of MB = −18.79±0.16. This fainter turn–over magnitude. We shall however not correct result suggests different possibilities. for this effect but include it in the systematic error budget. Branch, Romanishin and Baron (1996) have recently es- The metallicity dependence of the turn–over is better tablished a number of statistical correlations between the quantified (Ashman, Conti & Zepf 1995). In the Milky Way, parameters derived from the analysis of the light-curves the GCLF is dominated by clusters with [Fe/H]≃ −1.4 and spectral evolution of SNeI-a [e.g. B(max)–V(max), rate dex. In NGC 1380, Kissler-Patig et al. (1997) identified of decline, expansion velocity of SiII absorption line] and two populations of globular clusters. One matching the halo the colour of the respective parent galaxies. These authors population of the Milky Way, the other being more metal find that the SNeI-a in early type galaxies are on aver- rich ([Fe/H]=−0.2 ± 0.5). As we used one sample (mean age (even after disregarding sub-luminous objects such as [Fe/H]=−0.6±0.5) including both populations to derive the 1991bg) fainter than Ia in ‘spirals’ by ∼ 0.3 ± 0.1 with

GCLF above, based on metallicity alone, the correction to σMB (max) = 0.23. By taking, as zero point of the calibra- 0 apply to MV should be of the order of 0.2 ± 0.1 to fainter tion, the absolute magnitude of SNeI-a in late type galaxies, magnitudes. However, as shown in Kissler-Patig et al. (1997) i.e. MB = −19.53 ± 0.07 (Tammann et al. 1996), obtained the two populations have identical turn–overs in V , compati- via Cepheid distances with HST, it seems that Ia in ‘early’ ble (also in B and R) with a slightly younger red population, type galaxies should have MB ≈−19.2±0.2. With these fig- compensating the metallicity effect with an age effect. The ures taken at face value, SN 1992A might be about one half correction should therefore be reduced to less than 0.1 mag, magnitude fainter than expected, and therefore one could that we neglect and include it in our random errors. conjecture about its possible peculiarity. However we note In summary, we end up with a mean distance modulus the following. Subluminous SNe such as SN 1991bg (Filip- of (m−M) = 31.35±0.16, keeping in mind that two possible penko et al. 1992a, Leibundgut et al. 1993, Turatto et al. systematic errors (different MV (HB)–[Fe/H] relation, weak 1996 ) or SN 1992K (Hamuy et al. 1994) are clearly identi- galaxy type effect between S0 and spirals) are not included, fiable as peculiar objects from their own spectroscopic evo- but could only act to lower the distance modulus up to 0.3 lution (e.g. redder continuum, lower photosperic expansion mag. The distance modulus corresponds to a distance of velocity). This is not the case for SN 1992A. Indeed its spec- 18.6 ± 1.4 Mpc. troscopic evolution (Kirshner et al 1993, Suntzeff 1996), is Further comparison can be made with the turn–over typical of normal SNeI-a (e.g. Branch, Fisher, Nugent 1993). values and distances (using the above calibration) of other In addition, Patat et al. (1996) have shown, in a convincing Fornax members (Tab. 4). way (see their Fig. 8 ), that the spectroscopic evolution (at The weighted mean of the distances of Tab. 4 gives early stages) of SN 1992A is almost identical to that of the (m − M) = 31.35 ± 0.09 (1σ) or D = 18.6 ± 0.8 Mpc. spectroscopically normal SN 1994D. The photometric data The comparison between the ±3σ range with each distance, provide a quite contradictory picture. SN 1994D achieved might suggest that these members form a distribution of at maximum B=11.60 and V=11.72 after the small correc- Fornax cluster elongated along the line of sight by less than tion to the apparent magnitude at maximum to account for ±14%, but all the derived distance moduli include the mean an E(B–V)=0.06. Unfortunately the distance to its early within the errors supporting previous claims that Fornax is type (E7) parent galaxy, NGC 4526, has not been mea- a very compact cluster. sured directly. One might tentatively assume that the dis- The V turn–over magnitude for NGC 1380 falls well tance of NGC 4526, a bona fide member of the Virgo cluster within the range spanned by the other Fornax galaxies. Ex- (Sandage, Binggeli et Tammann 1985), presumably ranges cluding NGC 1399, the central giant cD for the reasons given between 17.1 Mpc of NGC 4321 (Freedman et al. 1994) and above (e.g. Harris 1997), and the second brightest galaxy 25.5 Mpc of 4639 (Sandage et al. 1996). Both measures are NGC 1404 (see Richtler et al. 1992 for its peculiar situation), based on the P-L relationship of Cepheids. After applying we note that the turn–over magnitude of the smaller galax- these distance moduli (with the attached errors) to the B ies is strikingly constant, supporting a weak dependence of mag at maximum of SN 1994D, one concludes that the abso- the turn–over luminosity with type among these galaxies. lute magnitude at maximum of SN 1994D presumably falls We note in passing that our derived distance modulus between MB = −19.34 and MB = −20.65. Although this of (m − M) = 31.35 ± 0.16 falls precisly at the mean of Tab. range of magnitude is quite large, this result would indicate 3, and agrees perfectly with the Cepheid distance to NGC that the magnitude at maximum of SN 1994D is consistent 1365. with either the average absolute at maximum derived above for SNeI-a in early-type galaxies or with the possibility that this SN could have been unusually bright at maximum. In all cases (assuming that NGC 4526 is a member of the Virgo cluster) the peak of light of SN 1994D is definitely brighter than that exhibited by SN 1992A. This implies that SNeI- 4 THE ABSOLUTE MAGNITUDE AT a which appear almost spectroscopically identical (at early MAXIMUM OF SN 1992A stages), can still span a range of maximum brightness of > SN 1992A is one of a few type Ia supernovae which have ∼ 0.5 mag. been discovered before maximum light, therefore the appar- ent magnitude at maximum light has been measured with great accuracy. The B maximum occurred on January 19, 1992 at B = 12.56±0.02 and (B −V ) = 0.00±0.02 (Suntzeff

c 0000 RAS, MNRAS 000, 000–000 Globular Cluster Calibration of SN 1992A 5

Table 4. Distance to individual galaxies in the Fornax cluster

Galaxy TO(V) (m − M)V Hubble type Method References

NGC 1344 23.80 ± 0.25 31.42 ± 0.32 E GCLF 1 NGC 1365 – 31.32 ± 0.20 SBb Cepheids 2 NGC 1374 23.48 ± 0.15 31.10 ± 0.25 E GCLF 3 NGC 1379 23.66 ± 0.30 31.28 ± 0.37 E GCLF 3 NGC 1380 23.67 ± 0.13 31.29 ± 0.16 S0 GCLF this work NGC 1399 23.81 ± 0.09 31.43 ± 0.22 E (Cd?) GCLF 4 NGC 1404 24.01 ± 0.14 31.63 ± 0.24 E GCLF 1,5 NGC 1427 23.70 ± 0.20 31.32 ± 0.28 E GCLF 3

1: Blakeslee & Tonry, 2: Madore et al. 1996, 3: Kohle et al. 1996, 4: Whitmore 1997, 5: Richtler et al. 1992.

5 THE ABSOLUTE MAGNITUDE AT et al. 1992, Saha et al. 1994), SN 1972E (Saha et al. 1995), MAXIMUM OF SNEI-A IN EARLY TYPE SN 1981B (Saha et al. 1996a), SN 1960F (Saha et al. 1996b), GALAXIES SN 1990N (Leibundgut et al. 1991, Sandage et al 1996), we have extracted the B absolute magnitude at maximum from Differences in the photometric evolution of type I SNe were Tammann (1996) [for 1981B we have used the re-calibrated first pointed out by Barbon et al. (1973) and Pskovskii apparent magnitude at maximum (Patat et al. 1996), for (1967). The latter author also suggested that the absolute SN 1990N the new data come from Lira et al. (1998)], the magnitude at maximum of type I SNe correlates with the ∆m(15) are from van den Bergh (1996) and Schaefer (1996a, rate of decline (β) in such a way that: the faster the early 1996b, 1996c). decline of a SN the fainter its absolute magnitude at max- Fig. 6 shows the plot of the absolute magnitude at max- imum. However, owing to the difficulties in measuring β imum MB as a function of ∆m(15). Circles represent SNe even in the best observed objects (e.g. Hamuy et al. 1991), in Spirals, triangles SNe in early type galaxies. We have such a relationship has been the subject of debate for some computed the best-fit regression by using a least squares fit, time. Phillips (1993), by using as a tracer of different rates taking into account the errors in both coordinates, and we of decline the total drop in magnitude that a SN under- obtain: M = 2.40 ± 0.33(1σ) × ∆m(15) − 22.06 ± 0.41(1σ) goes from its peak brightness until 15 days after maximum B Light symbols in Fig. 6 (not used in computing the fit) light [∆m (B)], has considerably improved the situation 15 represent SNe of Tab.6 for which no individual distances to (see also Maza et al. 1994 and Hamuy et al. 1995). From his the parent galaxies, obtained via GCLF or Cepheids, are Fig. 1 (top) a clear relationship between ∆m (B) and the 15 available. absolute magnitude at maximum seems to exist. However, The slope of our fit is similar to that obtained by Sandage et al. (1996), by studying the absolute magnitude Phillips (1993), though only 4 objects are in common at maximum and the rates of decline of a sample of type (1990N, 1981B, 1991bg and 1992A). The Phillips’s inter- Ia SNe occurring in late-type galaxies concluded that There cept is fainter by ∼ 0.4 magnitudes, possibly reflecting dif- is no clear relation between the absolute magnitudes.... and ferences in the zero point of the methods used to determine the decay rates (see also H¨oflich et al. 1996). The existence the distances to each parent galaxy. i.e. Surface Brightness of this discrepancy motivates our analysis. We have collected Fluctuation and Tully-Fisher in Phillips and Cepheids and from the literature (Tab. 5) the following data for SNeI-a ful- GCLF in this paper. filling the following requirements: a) to have been observed If one restricts the analysis only to the prototypical at maximum (or near maximum) with a reasonable photo- SNeI-a [ as defined by Branch, Fisher and Nugent (1993) metric error; b) the individual distances to the parent galax- or Branch and Tammann (1992)] which are the only ones ies to be measurable via Cepheids (for spirals) and GCLF actually usable to determine the distances, one has to per- (for early types). In addition we have determined (from the form the fit after excluding SN 1991bg (dashed line in Fig. original data) the apparent magnitude and the rates of de- 6). In this case we obtain a considerably less steep slope cline of 3 ‘historical’ SNe (SN 1919A, 1939A and 1957B) and a fainter intercept M = 1.52 ± 0.42(1σ) × ∆m(15) − because the TO magnitudes of the GCLF of their parent B 21.07±0.49(1σ). However, these data can be more profitably galaxies have been determined, in recent years (see Whit- used to improve the zero point of the relationship found by more 1997 and references therein). Hamuy et al. (1996) whose slope has been determined on 26 The selected objects are listed in Tab. 5 which gives the SNe whereas the zero point is based on 4 SNeI-a (1937C, SN designation with the parent galaxy (col. 1); the apparent 1972E, 1981B, 1990N) which all appeared only in late type magnitude at maximum (col. 2); the rate of decline (col. galaxies. We have fitted our data points by adopting the 3); the adopted turn-over magnitude (col. 4); the distance Hamuy’s slope (0.784) and assuming as zero point the value modulus derived by using our TO value, see Tab. 3, (col. of the intercept which minimizes the reduced χ2 (1.03). This 5); the absolute B magnitude⋆ at maximum (col. 6) and the fit (solid line in Fig. 6) yields: references (col. 7). For SNe Ia calibrated by Cepheids, i.e. 1937C (Sandage MB = 0.784 ± 0.18(1σ) × ∆m(15) − 20.24 ± 0.24(1σ) [1]

⋆ The photographic magnitudes have been reduced to the B band through the colour equations provided by Arp (1956)

c 0000 RAS, MNRAS 000, 000–000 6 M. Della Valle et al.

Table 5. Data for SNeI-a whose distance has been measured through the use of the peak of the GCLF

SN m(max) ∆m(15) TO(V) (m − M)◦ MB Ref.

1919A(N 4486) 12.2(pg)±0.2 1.15±0.10 23.88 ± 0.07 31.50±0.21 −19.1 ± 0.3 1,2,3,4,16 1939A(N 4636) 12.4(pg)±0.35 1.5±0.2 24.18 ± 0.20 31.77±0.28 −19.2 ± 0.45 5,6,7,8,16 1957B(N 4374) 12.4(pg)±0.3 1.3±0.2 24.03 ± 0.3 31.65 ± 0.36 −19.05 ± 0.47 9,10,11,12,13,16 1980I(N 4374) 12.7B±0.1 – 24.03 ± 0.3 31.65 ± 0.36 −18.95 ± 0.37 16,17 1991bg(N 4374) 14.75(B)±0.1 1.95±0.05 24.03 ± 0.3 31.65 ± 0.36 −16.90 ± 0.37 13,14,16 1992A(N 1380) 12.56(B)±0.02 1.47±0.05 23.67 ± 0.11 31.35 ± 0.16 −18.79 ± 0.16 15,16 unweighted mean⋆ −19.02 ± 0.16 weighted mean⋆ −18.91 ± 0.12

1: Baade 1936, 2: Baade 1938, 1941, 3: van den Bergh 1961, 4: Whitemore 1997, 5: Baade 1941, 6: Hoffleit 1939, 7: Giclas 1939, 8: Kissler et al. 1994, 9: Bertola 1964, 10: G¨otz 1958, 11: Romano 1957, 12: Li Tzin 1957, 13: distance derived from Ajhar et al. 1994, 14: Turatto et al. 1996, 15: Suntzeff 1996, 16: this paper, 17: Barbon et al. 1989. ⋆ after excluding SN 1991bg

Table 6. Data for SNe for which no distance to the parent galaxy (iii) The similarity of the absolute magnitude at maxi- via Cepheids or GCLF is known. mum of 1992A with that of 1981D and 1980N might be only illusory. In fact, if one compares the GCLF and PNLF dis-

SN MB ∆m(15) Ref. tances of NGC 1399 and N 1404, both belonging to Fornax, a difference, (m–M)GC –(m–M)P Ne ∼ 0.3−0.4 mag, between 1980N –18.86±0.29 1.20±0.10 1,2 the distance scale zero points seems to exist (if we extend 1981D –18.76±0.29 1.15±0.10 1,2 this analysis to NGC 4374 and NGC 4486, belonging to the 1989B –19.51±0.21 1.31±0.07 3,4 ± . ± . Virgo Cluster, ∆m increases up to 0.6–0.7 mag). In turn this 1991T –19.94 0 23 0.94 0 07 5,6 ∼ − 1994D –19.88±0.66 1.26±0.05 7 would imply that 1981D and 1980N have MB (max) 19 and NGC 1316 should be placed on the far-side of the For- 1: Sandage & Tammann 1996, 2: Hamuy et al. 1991, 3: Tammann et al. nax cluster (like NGC 1404). This possibility is not entirely 1996, 4: Wells et al. 1994, 5: van den Bergh 1996, 6: Phillips 1993, 7: Patat ruled out considering that NGC 1316 is located in the south- et al. 1996 ern extension of the Fornax cluster and not in the tight main concentration where all the other Fornax galaxies presented 6 DISCUSSION in Tab.3 are located. In this scenario only 1992A would be moderately sub-luminous. Two other SNeI-a have appeared in the Fornax cluster: 1980N and 1981D, both in NGC 1316. Their peak lumi- nosities were B(max)=12.49 and B(max)=12.59 (Hamuy et al. 1991, Sandage and Tammann 1996). The only direct measurement of the distance of their 7 CONCLUSIONS parent galaxy comes from the Planetary Nebula Luminos- ity Function (=PNLF; see Tab. 7). By combining the dis- In this paper we have determined the distance to NGC 1380, tance modulus provided by McMillan, Ciardullo and Ja- an S0 galaxy host of the type Ia SN 1992A, through the use coby (1993) and Jacoby (1997) with the respective apparent of the TO magnitude of the GCLF. We find a distance mod- ± ± magnitudes at maximum, we derive MB = −18.69 ± 0.12 ulus of 31.35 0.16 corresponding to a distance of 18.6 1.4 and MB = −18.59 ± 0.12, in good agreement with MB = Mpc. This is consistent with the distances to other members −18.79 ± 0.16 of SN 1992A. of the Fornax cluster, utilizing the same method, as well as This result suggests a number of possible alternative the Cepheid distance to NGC 1365. interpretations: By applying this distance to the apparent magnitude of SN 1992A, we find that at peak brightness SN 1992A reached (i) Spectroscopic normal Supernovae Ia in early type MB = −18.79 ± 0.16, which is about 0.4 mag fainter than galaxies can be fainter, by ∼ 0.7 − 0.8 mag, than Super- expected for typical SNeI-a in early type galaxies (Branch, novae in Spirals (see also van den Bergh and Pazder 1992). Romanishin and Baron 1996), and about 0.7 magnitudes (ii) As an alternative one might consider that the absolute fainter than SNeI-a in spirals, if one accepts as zero point magnitudes at maximum of SNeI-a adopted in this paper MB = −19.53 ± 0.07 (Tammann et al. 1996), the absolute for late type galaxies are ‘too bright’. Since the Sandage et magnitude at maximum of SNeI-a in Spirals. al. group makes use of multicolor photometry to determine It is worthwhile noting in this respect that recent work the P-L relationship of Cepheids, one can immediately rule by Mazzali et al. (in preparation) shows a good correlation out the effect of reddening. On the other hand, the effect between the velocity widths of the nebular lines (at around of the metallicity on the P-L relation is still poorly known 300 days after the maximum) and the rate of decline (and (e.g. Kennicutt et al. 1998). Chiosi, Wood and Capitanio therefore the absolute magnitude at maximum). The veloc- (1993) predict a small sensitivity of the P-L relationship to ity widths for SN 1992A would indicate that it is sublumi- metallicity, while a recent work by Beaulieu et al. (1997) nous relative to other normal type Ia supernovae. might even indicate an opposite trend (see also Efremov The close similarity with the apparent magnitude at 1996). maximum exhibited by SN 1980N and SN 1981D, two other

c 0000 RAS, MNRAS 000, 000–000 Globular Cluster Calibration of SN 1992A 7

Table 7. Data for SNeI-a whose distance has been measured through the use of the PNLF

SN Galaxy (m − M)◦ MB ∆m(15) References

1980N NGC 1316 31.19 ± 0.07 −18.69 ± 0.12 1.2±0.1 1,2,4,5 1981D NGC 1316 31.19 ± 0.07 −18.59 ± 0.12 1.15±0.1 1,2,4,5 1957B NGC 4374 31.04 ± 0.18 −18.53 ± 0.21 1.3±0.3 3,2,4,5 1980I NGC 4374 31.04 ± 0.18 −18.33 ± 0.21 – 3,2,4,5 1991bg NGC 4374 31.04 ± 0.18 −16.13 ± 0.21 1.95±0.05 3,2,4,5 1960R NGC 4382 30.85 ± 0.17 −18.95 ± 0.25 1.2±0.1 3,2,4,5,6 1919A NGC 4486 30.79 ± 0.17 −18.49 ± 0.21 1.15±0.1 2,4,5 unweigthed mean⋆ −18.60 ± 0.21 weigthed mean⋆ −18.60 ± 0.07

1: McMillan, Ciardullo & Jacoby (1993), 2: Jacoby (1997) 3: Jacoby, Ciardullo & Ford (1990), 4: this paper, 5: Barbon et al. (1989), 6: Bertola (1964), ⋆ after excluding SN 1991bg

SNeI-a in the Fornax Cluster, could indicate that SN 1992A that the MB vs. ∆m(15) relationship becomes nonlinear for is a peculiar object only if NGC 1316, the parent galaxy high rate of decline (see also the case of SN 1992K pointed of SN 1980N and 1981D, is placed on the far side of the out by Hamuy et al. 1995). cluster at d ∼> 20.5 Mpc. In this case the absolute magni- 3) We find a difference of ∆m = 0.31 ± 0.14 mag be- tudes of SN 1980N and SN 1981D would be slightly brighter tween the absolute magnitude at maximum of SNeI-a cal- than MB ∼ −19, in agreement, within the errors, with the ibrated with GCLF and PNLF (see Tab. 6 and Tab. 7). value reported by Branch, Romanishin and Baron (1996) for To check the significance of this result we have compared SNeI-a occurring in early type galaxies. Finally, we are not the distance moduli of the ten galaxies for which the dis- certain that all necessary corrections were made to the TO tances have been determined via PNLF and GCLF (see magnitude of the GCLF to guaranty its reliability as stan- Tab. 1 of Jacoby (1997) and Whitmore 1997). By using dard candle. Indeed, in section 3 we discussed systematic the TO mag reported in our Tab. 3 we find a difference effects which could conspire to make the TO magnitude of (m-M)GC –(m-M)P Ne = 0.56 ± 0.24 (and (m-M)GC –(m- NGC 1380 fainter by ∼ 0.3 mags. M)P Ne = 0.61±0.19 after excluding NGC 3379). This result We have derived the absolute magnitude at maximum may put doubt on the consistency of the zero points of these of a number of historical SNeI-a which have occurred in distance indicators. However, if we assume as calibrator of early type galaxies, whose distances are known through the the absolute magnitude at maximum of SNeI-a in early type GCLF. Together with high quality data, collected from the galaxies the data provided by PNLF ( Tab. 7), the price literature, we have produced a linear fit to the data points to pay to fit the AMMRD with 0.784 slope (Hamuy et al. in the ∆m(15) vs. MB plane. We find a slope similar to that 1996) is to make considerably fainter the absolute magni- ∼ − measured by Phillips (1993). The ∼ 0.4 mag difference in tude at maximum of SNeI-a in spirals, close to MB 19. the intercept probably reflects the zero point difference ex- We note that Kennicutt et al. (1998) have estimated that isting between the distances obtained via Cepheids/GCLF metallicity effects on the distance scale derived with HST (adopted in this paper) and Surface Brightness Fluctuation observations of Cepheids could affect the distance moduli, ∼ and Tully-Fisher methods (adopted by Phillips 1993). After to the respective parent galaxies, only at 0.2 mag level. excluding SN 1991bg from the fit and adopting the slope de- At least four critical observations could significantly im- rived by Hamuy et al. (1996) we have determined a new zero prove our present understanding of the problem: −1 −1 point for this relationship and H◦ = 62±6kms Mpc . It a) determination of the distance of NGC 1316, parent is apparent that any correction for reddening would tend to galaxy of SN 1980N and 1981D, through the use of the increase the obtained value of H◦. Our plot in Fig. 6 shows GCLF (the PNLF distance already being available). This that: should also enable us to clarify whether or not SN 1992A is 1) SNeI-a in Spirals are located in the bright and slow a peculiar (sub-luminous) object, despite its ‘protonormal’ part of the diagram whereas the SNe in early type galaxies spectroscopic evolution. fall in the faint and fast part of the plot. Owing to the in- b) determination of the distance of NGC 1380 via the trinsic dispersion of the relationship, it is apparent that an PNLF to make a sensible comparison with the distance ob- analysis based only on SNe discovered in Spirals or in early tained via GCLF in this paper. type galaxies would hardly reveal any correlation between c) determination of the distance to NGC 4526, parent the rates of decline and absolute magnitude at maximum, galaxy of SN 1994D, through the use of the GCLF and then indicating that the dependence of the absolute magni- PNLF. This SN may be a conspicuous exception to the tude at maximum on ∆m(15) and on the Hubble type of the AMMRD relationship, unless we assume that NGC 4526 is parent galaxies are almost equivalent. On the basis of data located on the near side of the Virgo cluster at ∼ 13 Mpc reported in Tab. 5 (but excluding 1991bg), the unweighted (see Tonry 1995). However, this last possibility appears quite mean of the absolute magnitude at maximum of SNe Ia in unlikely, because it is known that early type galaxies are early type galaxies is MB = −19.05 ± 0.16. By comparing normally concentrated towards the core of the clusters. As this figure with MB = −19.53 ± 0.07 (Tammann et al. 1996) an alternative, NGC 4526 may not belong to Virgo Cluster, for Ia in Spirals, we obtain ∆M = 0.48 ± 0.17. rather being a foreground galaxy. 2) Sub-luminous objects such as 1991bg would indicate d) measurement of the distance, with Cepheids, to NGC

c 0000 RAS, MNRAS 000, 000–000 8 M. Della Valle et al.

3627 and NGC 4527, parent galaxies of SN 1989B and SN Filippenko, A.V., Richmond, M.W., Branch, D., Gaskel, C.M., 1991T. Indeed, these objects have been well studied, close Herbst, W., Ford, C.H., Treffers, R.R., Matheson, T., Ho, to maximum, in the past (Barbon et al. 1990, Wells et al. L.C., Dey, A., Sargent, W.L.W., Small, T.A., Bruegel, W.J.M. 1994, Phillips et al. 1992, Ruiz-Lapuente et al. 1992, Filip- 1992a, AJ, 104, 1543 penko et al. 1992b), and therefore, once their position in the Filippenko, A.V., Richmond, M.W., Matheson, T., Schields, J.C., Burbidge, E.M., Cohen, R.D., Dickinson, M., Malkan, M.A., MB vs. ∆m(15) plane is firmly established, the large error Nelson, B., Pietz, J., Schlegel, D., Schmeer, P., Spinard, H., still associated with the intercept of [1] will be considerably Steidel, C.C., Tran, H.D., Wren, W. 1992b, ApJ, 384, 15 reduced. 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Figure 1. The NGC 1380 galaxy (B 15000 s). Figure 3. Globular cluster luminosity function in V . Symbols as for B.

Figure 2. Globular cluster luminosity function in B. The solid curve shows the best Gaussian fit, the dashed curve the best fit of Figure 4. Globular cluster luminosity function in R. Symbols as for B. a t5 function. The dotted lines show the 60% completeness limit in B (left) and in BV R (right).

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Figure 5. Globular cluster luminosity functions in B,V,R of the Milky Way as derived from the McMaster University globular cluster database.

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Figure 6. The Absolute Magnitude at Maximum vs. Rate of decline relationship for SNeI-a. The filled symbols represent the objects whose individual distances have been measured via Cepheids (circles) or GCLF (triangles). The light symbols represent SNe for which the individual distances via Cepheids or GCLF are not available, therefore the average distance of the respective cluster has been used. These SNe have not been used to compute the best fit. The solid line represents the best fit (without SN 1991bg) after assuming the Hamuy et al.’s (1996) slope of 0.784. The dashed line is the best-fit obtained by using a least squares fit which takes into account the errors in both coordinates (slope 1.52).

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