L25 The Astrophysical Journal, 671: L25–L28, 2007 December 10   2007. The American Astronomical Society. All rights reserved. Printed in U.S.A. CONSTRAINTS ON CIRCUMSTELLAR MATERIAL AROUND THE TYPE Ia SUPERNOVA 2007af 1,2 Joshua D. Simon, 3 Avishay Gal-Yam, 3,4 Bryan E. Penprase, 5 Weidong Li, 6 Robert M. Quimby, 7 Jeffrey M. Silverman, 6 Carlos Allende Prieto, 7 J. Craig Wheeler, 7 Alexei V. Filippenko, 6 Irene T. Martinez, 5 Daniel J. Beeler, 5 and Ferdinando Patat 8 Received 2007 September 6; accepted 2007 October 18; published 2007 November 8 ABSTRACT Patat et al. recently inferred the existence of circumstellar material around a normal Type Ia supernova (SN Ia) for the first time, finding time-variable Na i D absorption lines in the spectrum of SN 2006X. We present high- resolution spectroscopy of the bright SN Ia 2007af at three epochs and search for variability in any of the Na D absorption components. Over the time range from 4 days before to 24 days after maximum light, we find that the host-galaxy Na D lines appear to be of interstellar rather than circumstellar origin and do not vary down to the level of 18 m (column density of cm ). We limit any circumstellar absorption lines to be weaker than 11 -2 ˚ A 2 # 10 ∼10 m ( cm ). For the case of material distributed in spherically symmetric shells of radius ∼10 16 cm 10 -2 ˚ A 6 # 10 surrounding the progenitor system, we place an upper limit on the shell mass of ∼ , where X is -8 (3 # 10 )/XM , the Na ionization fraction. We also show that SN 2007af is a photometrically and spectroscopically normal SN Ia. Assuming that the variable Na D lines in SN 2006X came from circumstellar matter, we therefore conclude that either there is a preferred geometry for the detection of variable absorption components in SNe Ia, or SN 2007af and SN 2006X had different types of progenitor systems. Subject headings: circumstellar matter — supernovae: general — supernovae: individual (SN 2006X, SN 2007af) Online material: color figure 1. INTRODUCTION Type Ia supernovae (SNe Ia) are currently the only distance indicator that can be used effectively out to cosmological dis- tances (e.g., Riess et al. 1998, 2007; Perlmutter et al. 1999; Leibundgut 2004; Filippenko 2005). Therefore, understanding the nature of these explosions and any potential systematics that may be present is of great importance to cosmology. However, we still do not know what the progenitor systems of SNe Ia are, and observations suggest that there may be at least two physically different progenitor classes (e.g., Mannucci et al. 2005, 2006; Scannapieco & Bildsten 2005; Sullivan et al. 2006; Quimby et al. 2007), as well as some peculiar objects (e.g., Li et al. 2001, 2003; Hamuy et al. 2003, although see Benetti et al. 2006). Patat et al. (2007a) have recently made a possible breakthrough in the study of SN Ia progenitors by optically detecting circumstellar material (CSM) in a SN Ia for the first time. Using high-resolution 1 Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. 2 Based in part on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universita ¨t Mu ¨nchen, and Georg-August-Universita ¨t Go ¨ttingen. 3 Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MS 105-24, Pasadena, CA 91125; jsimon@astro.caltech.edu, avishay@ astro.caltech.edu. 4 Astrophysics Group, Faculty of Physics, Weizmann Institute of Science, 76100 Rehovot, Israel. 5 Department of Physics and Astronomy, Pomona College, 610 North Col- lege Avenue, Claremont, CA 91711; penprase@dci.pomona.edu. 6 Department of Astronomy, University of California, Berkeley, CA 94720-3411; weidong@astro.berkeley.edu, jsilverman@astro.berkeley.edu, alex@astro.berkeley.edu. 7 McDonald Observatory and Department of Astronomy, University of Texas, Austin, TX 71782; quimby@astro.as.utexas.edu, callende@astro.as.utexas.edu, wheel@astro.as.utexas.edu. 8 European Southern Observatory, Karl Schwarzschild Str. 2, D-85748 Garching bei Mu ¨nchen, Germany; fpatat@eso.org. spectra of SN 2006X spanning from just before maximum light to 4 months later, they showed that at least four distinct components of the Na i D absorption lines varied with time until ∼2 months postexplosion. Although similar behavior has been seen in Milky Way stars and is generally attributed to small interstellar clouds moving across the line of sight (e.g., Welty & Fitzpatrick 2001), in SN 2006X the lack of time evolution in the corresponding Ca ii H and K absorption features at the same velocities probably rules out that interpretation. Instead, Patat et al. conclude that the variable absorption is from circumstellar clouds in the progenitor system that were ionized by the radiation from the supernova and recombined several weeks later; because Na i has a much lower ionization potential than Ca ii , the Na i line profiles can change without an accompanying effect in the Ca ii lines if the ionizing radiation has an appropriate spectrum. These results appear to indicate a single- degenerate progenitor for SN 2006X with a red-giant companion. Multiple-epoch high-resolution spectroscopy is available for only one previous SN Ia, the peculiar SN 2000cx (Patat et al. 2007b), so it is not yet known whether the time evolution seen in SN 2006X is common. Assuming that the variable absorption is related to material from the SN progenitor, if the behavior of SN 2006X is not universal, then either there must be geo- metric effects that limit the visibility of the absorption to certain lines of sight (e.g., near the orbital plane of the progenitor system) or there are multiple progenitor systems for SNe Ia. In this Letter , we present high-resolution spectra of the Type Ia SN 2007af obtained at -4.3, +16.6, and +23.7 days relative to maximum light. We use these data to test the Patat et al. (2007a) model, searching for variability in the Na D absorption features. 2. OBSERVATIONS AND DATA REDUCTION SN 2007af was discovered by K. Itagaki on 2007 March 1.84 (UT dates are used throughout this Letter; Nakano & Itagaki 2007). A spectrum obtained on 2007 March 4.34 showed that SN 2007af was a SN Ia at least a week before